oh, that's easy. they're able to brace themselves if... they'd be able to brace themselves. a minifig standing ground in a single spot can. a minifig flying through the air or loosely holding onto a ladder cannot.
Yeech. I don't like the knockback rules in Brikwars... I find it rather redundant constantly figuring out MoM and PoP for everything. I just ignore knockback in general and fudge it in when appropriate or needed. If the defendant's defense score was 1 point greater than what he needed to survive, or exactly enough, then he gets floored (and drops his gear). Otherwise he staggers but bounces back, good as new. Simple, effective, entertaining.