IIRC, knockdown gives a -100 dodging penalty
dodging in this game seems to work through values like that, so a person who is knocked down will almost never dodge anything, but add something like evasive aura on top of other dodging/miss values and you might still miss them
in the same way, your character can use uncanny evasion but be flanked and still get hit
not sure if that pertains to the scenarios you're describing
