So Minecraft calculates the ability to critical hit when you are falling when landing a hit, but the way it seems to calculate that is based on the speed the player is falling as far as I'm aware, since the vanilla slowfalling effect prevents the critical damage from being applied despite still showing the particles associated with landing a crit.

This issue extends to the Wings from this mod, since they give a form of slowfalling, it's nearly impossible to crit consistently while having wings. This is quite a problem for combat, and since patching the entire critical formula may be a bit beyond the scope of this mod, I suggest making the slowfall effect only apply when the player is holding Sneak while falling, and instead have the wings passively negate fall damage.

good idea