I solved the problem...sort of...with the insert. I'm not supposed to be lifting anything heavy or doing a lot of bending, etc., so I didn't want to risk taking my (heavy) machine off and on the platform to try to adjust the chains. Instead, I got a couple thin books from my sewing collection and slipped them under the machine. It raised the machine enough that the insert fits better. The machine bed is a tiny bit higher then the insert but it's not enough to fuss around with it any more. I may use Washy tape to smooth out the slight hump.