Thank you for your feedback! In the game, we did not tell which part remains active. In general, during normal movement, the largest detached part remains active. If the separation occurs when ability is used, then the part that has this special block will be active. I hope I explained correctly)
I was a level designer and I agree with you. We could make more levels that would better prepare the player for new situations. But it seemed to us that 17 levels is a lot. Although the game still has level 18 in the credits as an extra level.