I notice up doesn't make you jump. There's nothing wrong with having space let you jump too, but you really ought to make it so you can jump with up. It fits the pattern of press a direction button to go in that direction.
Also, the enemy's paths are unpredictable. Sure you can sit there and wait to see when they turn around, but that's boring. It's better to be something predictable like they turn when they hit the end of the platform.