Any pics of the molle express on body? I'm on the shorter side at 5'7" so thinking this bag will fit ok. With the G2 Zulu, it took me a while to get it fitted right but once it was it fit great. For some reason, these packs just take more effort to get them set up and fitted properly.
in my experience, with the packs with the 24" stays and longer there's no effort required to get it to fit properly - just put it on, pull all straps tight and it's instantly comfortable. with the mollex, there's no adjustment i can make to make it comfortable - pull the shoulder straps to where it feels right and the waist belt is way up on my belly button...but if i adjust the waist belt so it's right at the illiac crest then i have the shoulder straps so loose that it feels like a lumbar pack.
i understand the really short stays like the x-ray where it's designed so soldiers can carry it on their load-bearing vest or way above their weapon belt...but the packs like the mollex, zulu, etc. where the chances are high the user will use it with a waist belt, the suspension is really lacking compared to the navigator, zxr, etc. i apologize for the rant - it's directed at kifaru, not you

you're lucky you like the way the zulu fits you/your torso length matches it and in that case, the mollex shouldn't be any different.
just the kifaru doobie inside to puff it out...i'm 5'9":
ku3700 on the left, mollex in the middle, and the zxr on the right. both the ku3700 and the zxr have 24" stays and the ends are about 2" above my shoulder. the mollex stays are about 3" below my shoulder already with just the doobie inside. if i put just 10 lbs inside the mollex the whole pack sags even lower because the stays aren't supported directly by the waist belt.
in comparison, the osprey kestrel 28/38 has excellent shoulder lift too - in this case, it's already loaded down with day hike gear.