Hard to say for sure without video but IMO you're probably not actually boosting off the lip with your legs. You're probably being too passive which means your back wheel kinda goes into the lip rather than pushing off it. When that happens you end up rotating forward and landing front heavy. Being too passive on the jump provides at least 3/4 of every Pinkbike Friday Fails.
It probably is a little more difficult to get the "meercat" position going on a bike that's too big but all the little kids I see sending stuff on their Dad's bike tells me it's not impossible.