Did some testing
The armor itself seems to be consistent once its out, but it takes 18 frames to be active (when the smoke effect and controller rumble starts) which at first made me think it grew stronger over time, maybe that's what you're experiencing?
Some other properties I found:
- Moves hitting the armor do 4/5 of their normal damage.
- Breaking the armor is just based on the % your opponent's attack deals. The threshold is either 14.4% or 14.5% after damage reduction. Any hit that does less % than that does no knockback no matter how far it would have sent you without the armor.
- The armor will still work through multiple hits as long as no individual hit would have broken the armor on its own. e.g. Cloud's cross-slash does well over the damage threshold in total but will not break through the armor.
- The armor does not stop capes, windboxes, paralysis, or sleep, but it does prevent being buried as long as the burying move does not cross the damage threshold. e.g. an un-inked Plant will not be buried by Inkling's roller, but a completely inked Plant will.