Overwatch is one of things that currently force players into Alpha-Striking - player is not able to deny space during AI turn, therefore its usually best to break line of sight instead of overwatching and getting one shot off.. While in beginning of the game, OW shots are OK, with late game, single burst is no longer viable option...
Therefore i think it would be best, if number of overwatch shots would depend on how many AP character had when Overwatch was activated. This way, Player could exchange his turn to act in AI turn via overwatch shots, which would allow him to set up defensive perimeters instead of focusing on alpha strike tactics..