Cause?

I record guess factors and displacement vectors for all waves, and come kNN time, I drop data with a (scaled to current situation) displacement vector that leads off the battlefield.

"If it's just for bounds checking, that doesn't make much sense to me in movement." Exactly. Basically, I need to add a boolean argument to that method so that my gun can drop points and my movement doesn't have to. After all, few if any enemies will be doing such culling, so not doing so with movement data will be a closer approximation to the enemy's view of the situation.