It's okay, but flying enemies SHOULD NOT go through walls. It makes it far too hard to attack them if they're coming from below, and also makes them virtually unavoidable.
@Flashed_Gordon: There is a crate which lowers the number of enemies that come at you in a wave. For some reason, this lowers the wave counter as well. This crate can be a nuisance if you're aiming to get the Hard Badge.
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