I had problems with tucks and it didn't seem to matter what the method was for sandwiching. I discovered......
It was my sewing machine. Even with a walking foot, I'd get tucks on the back. So.....
I now use a 1916 Singer 127 handcrank. ..... no tucks, beautiful stitches..... problem solved. And for FMQ, I use a Singer 1952 15-91.... drop the feed dogs, use the darning foot..... again, beautiful stitches, no problem. It was that $$$$ machine..... I just use that for mending now.