Tummy snap one tighter than legs? Im not sure what you mean. I have them done up in different positions, but the top and bottom snap line up, not always left and right are even though. I fine this on all the side snapping nappies, I do the first side and then the second side is uneven, but if i change it they're both uneven

I have used the ecos with success before, i think maybe he is just growing our of the small size. He was in a medium bubblebub today as well
Do the leg snaps up first, both ones, then do the tummy ones up as tight as you need. You might find that the tummy is on the tightest setting, the legs are on the second snaps out. This is the joy of side snaps. I always do the legs up first because you get a better fit