There are still mechanics of miracle resonance that are not understood, and if anyone's interested you could solve some of its remaining mysteries. As far as I know, the most comprehensive information comes from earlier testing I did, which resulted in this page here.
I could only test so much being on the PS3, where miracle resonance remains bugged. Here are three problems that I think can be figured out by people on PC and Xbox:
1. Confirming / refuting that a double boost is possible without the Ring of the Sun Princess
My current explanation of the 'double synergy boost' is as follows-
I came to the above conclusion by testing the permanent resonance signs in the catacombs. Standing in the middle of both puts you in range of both of them, and does not give you the double boost. It's possible that I could be incorrect, though, if actual resonance signs created by other players work a little bit differently, or if it's simply a matter of the rings needing to be even closer to each other.
HOW TO TEST THIS:
1. Be on the lookout for miracle resonance signs. They appear most frequently in active PvP areas, and also near the Phalanx in the Painted World. It's a common spot for AoE miracles to be cast.
2. Have a miracle equipped (like heal, force, or WotG), but do NOT have a talisman equipped. It is easier to see the synergy-confirmation in the HUD when the miracle is greyed-out and unable to be used.
3. When you see a resonance sign appear, run up to it and watch to see the ring appear in your HUD.
4. Wait and hope a second resonance signs appears near you without moving away from the sign you're already near. If one appears, watch to see if the ring in your hud becomes thicker (if it does work, it'll take a second or two).
In other words, to confirm this, you'll need to carefully watch the white ring that appears over your miracles icon in the HUD (needs to be one of the 9 miracles capable of synergy, some won't work). The difference between the thinner ring (single synergy boost) and thicker ring (double synergy boost) is subtle, so you'll have to pay close attention and literally watch the ring change size to be certain if it's the double boost.
2. How long miracle resonance signs last, and/or if using one makes it disappear
Watching some live streams, it appears that miracle resonance signs last for roughly 30 seconds. If anyone can watch and time them to see if they always last that long, or sometimes last for different amount of times, that would be great. This should be a very easy one to test.
I'm also curious if using a miracle resonance sign affects how long it lasts. Can it be "used up"? Will using a boosted miracle make the resonance sign disappear, or will it stay there for ~30 seconds no matter what?
3. The conditions for creating and seeing resonance signs
This is probably the most complicated task as it will require a partner, but I'm not sure that testing has been attempted so it might not actually be that difficult to solve. Based on a few things I've read, I have a few guesses as to the possible requirements:
-you may have to be within co-op range of the person casting the miracle
-it's possible that casting just any miracle might not work, and it may be limited to the nine miracles that are capable of miracle synergy
HOW TO TEST THIS:
1. Find a partner who is within co-op range.
2. Ensure you are connected by being able to see a summon sign from them.
3. Have one player run around and cast Force or Heal a bunch of times, with and without the summon sign down. See if the resonance signs show up for the other player.
If this works, you could then find out if those restrictions are even necessary. You could have one player cast miracles that aren't synergy-capable (DMB, the Lightning Spears, Gravelord Sword Dance...) to see if any miracle works, and also level up outside of co-op range and see if they still work.
I've also read older posts, from closer to when the game came out, that resonance signs appear to members of the same covenant. I don't think this was based on any testing and was just speculation, but incase you're having trouble seeing resonance signs from a partner, consider testing whether or not being the same covenant actually makes a difference as well.
I could only test so much being on the PS3, where miracle resonance remains bugged. Here are three problems that I think can be figured out by people on PC and Xbox:
1. Confirming / refuting that a double boost is possible without the Ring of the Sun Princess
My current explanation of the 'double synergy boost' is as follows-
However, someone has told me that they were pretty certain they received a double boost (as indicated by the thicker white ring that appears over your miracle's icon in the HUD), without wearing the ring.If you wear [the Ring of the Sun Princess] and stand near a resonance sign at the same time, the effect will stack as a 'double synergy boost'.
...
Two nearby resonance signs will not stack to create a double boost. A double boost requires combining a resonance sign with the Ring of the Sun Princess.
I came to the above conclusion by testing the permanent resonance signs in the catacombs. Standing in the middle of both puts you in range of both of them, and does not give you the double boost. It's possible that I could be incorrect, though, if actual resonance signs created by other players work a little bit differently, or if it's simply a matter of the rings needing to be even closer to each other.
HOW TO TEST THIS:
1. Be on the lookout for miracle resonance signs. They appear most frequently in active PvP areas, and also near the Phalanx in the Painted World. It's a common spot for AoE miracles to be cast.
2. Have a miracle equipped (like heal, force, or WotG), but do NOT have a talisman equipped. It is easier to see the synergy-confirmation in the HUD when the miracle is greyed-out and unable to be used.
3. When you see a resonance sign appear, run up to it and watch to see the ring appear in your HUD.
4. Wait and hope a second resonance signs appears near you without moving away from the sign you're already near. If one appears, watch to see if the ring in your hud becomes thicker (if it does work, it'll take a second or two).
In other words, to confirm this, you'll need to carefully watch the white ring that appears over your miracles icon in the HUD (needs to be one of the 9 miracles capable of synergy, some won't work). The difference between the thinner ring (single synergy boost) and thicker ring (double synergy boost) is subtle, so you'll have to pay close attention and literally watch the ring change size to be certain if it's the double boost.
2. How long miracle resonance signs last, and/or if using one makes it disappear
Watching some live streams, it appears that miracle resonance signs last for roughly 30 seconds. If anyone can watch and time them to see if they always last that long, or sometimes last for different amount of times, that would be great. This should be a very easy one to test.
I'm also curious if using a miracle resonance sign affects how long it lasts. Can it be "used up"? Will using a boosted miracle make the resonance sign disappear, or will it stay there for ~30 seconds no matter what?
3. The conditions for creating and seeing resonance signs
This is probably the most complicated task as it will require a partner, but I'm not sure that testing has been attempted so it might not actually be that difficult to solve. Based on a few things I've read, I have a few guesses as to the possible requirements:
-you may have to be within co-op range of the person casting the miracle
-it's possible that casting just any miracle might not work, and it may be limited to the nine miracles that are capable of miracle synergy
HOW TO TEST THIS:
1. Find a partner who is within co-op range.
2. Ensure you are connected by being able to see a summon sign from them.
3. Have one player run around and cast Force or Heal a bunch of times, with and without the summon sign down. See if the resonance signs show up for the other player.
If this works, you could then find out if those restrictions are even necessary. You could have one player cast miracles that aren't synergy-capable (DMB, the Lightning Spears, Gravelord Sword Dance...) to see if any miracle works, and also level up outside of co-op range and see if they still work.
I've also read older posts, from closer to when the game came out, that resonance signs appear to members of the same covenant. I don't think this was based on any testing and was just speculation, but incase you're having trouble seeing resonance signs from a partner, consider testing whether or not being the same covenant actually makes a difference as well.