I use 10mm retraction.I have not printed the tower yet , but i will. I think a need a raft in the beginning to make it really flat. Now after a while the bottom warps half way in.At the side of the machine it says remove top lid and open door when printing PLA but it hust made it worse.I need to check my speed settings i think. I printed with flashprint it went nice at the bottom but not the rest , i mean it was ok but it could be better/smoother.