Couple thoughts here guys,
If a suspension doesnt come back up all the way you could have a few things going on, first and foremost as already mentioned, weak springs. But also check all the pivot points on your front and rear arms, may sure they are free and not bent and binding.
And second, last year I did a lot of research on rear suspension, as i am also a big guy, eventually I upgraded to a used M10, and part of the M10 setup tells you is, for a bigger rider, where the rear scissor arm bolts to the slide rails, move it back 1 bolt hole ot so, that changes the geometry for a bigger guy. The M10 actually uses a sliding mechanism like whats used on the very rear idler wheels to tighten the track.
So on an factory setup, most rails have additional bolt holes already there, just seems that no one has told us why they are there!!