i know you have tried all the things suggested but i have two more one is fyi and that is when your piecing quilt make sure you stitches are not to small (tight) it will keep it from laying flat. the other thing that makes a big difference is i use the gloves that have a grip finish then i can keep the area i am fmq smooth with out a lot of mussel because i have arthur the gloves help me move my quilt without getting tired too soon it comes out nice and smooth.
good luck
hugs mema