Every moving object's X-Position subpixel carries over to the next object if both objects are in the same slot. There are 16 possible values (lowest 0, 16, ... , 240 highest) and this value means a lot for enemy manipulation.
Enemies can be manipulated by:
Optimizing your subpixel position (see Subpixel Carryover above)
Optimizing their subpixel position (see Subpixel Carryover above)
Delaying hits or using specific RNG manipulation
Using delays or manipulating the enemy spawn timer value (this affects which side of the screen they spawn on)