You are partialy correct, but thats my fault XD. The circular enemy acts how youve described, with the addition that the empty counterpart is where the full circle will appear on the next wave, but were ive made the mistake is the shield enemy, which is also empty but doesnt act the same way, to destroy it you must rotate the shield while the enemy is on top of it. But it makes so much more sense to keep it the way you have described on all enemy types, not just the circles.