ive tried a few things a while back on a melee combat. Best i found was just totaly ignore trying to utalize an actual collision system aspect.

Instead just useing a simple vec_dist for a min distance check and if attacking entity is facing in a particular arc angle to the target an attack can be made ( animation )

then just fall back on a mechanical RPG system to calculate a % chance to hit based on character level, stats and modifiers vs target level, stats, armor. doing the check 'to-hit; once per animation cycle then will solve the major problems