Having experience playing with and against SoFr decks, I think 25% may be a bit too much... But 10% might indeed be to low.
I think 17% would work well. That way with a full stack of 6 it caps out at ~100% like it should.
Does this seem good enough or would it still be to low?
It should be noted that if it goes too high too fast, some shields (like hope) will create OP combos.
I'm intentionally trying to keep it slightly less powerful than SoFr so that it is subtle enough to remain as a type "Other" card.
I recently posted a topic with a similar critique of SoFree:
Expanding Evasion MechanicsAnything with 100% defense is going to be OP if it has any significant place in the game. The same potentially applies to your card, which is -- I'm guessing -- why you made it <17% to begin with. However your card has the "advantage" that removing the shield makes the whole stack useless, as well as the potential for it to be UP for 1-point or lower shields.
Possible solution:
Chance to protect allies is 10% + 24%/R, where R is the damage reduction of the shield.
Dimensional Shield, Bone Wall, Wings, Dusk, and Fog all count as R=infinity.
Chance per Insignia:
Infinite: 10% + 0% = 10% (6 stacks is 60%)
(3-point) = 10% + 8% = 18% (6 stacks is 100%)
(2-point) = 10% +12% = 22% (5 stacks is 100%)
(1-point) = 10% +24% = 34% (3 stacks is 100%)
However this still offers only ~.3 - .5 reduction per Insignia, so I would probably make the cost 2|1