YOu don't need to ride more on your crotch. You torso position is not bad as is. You can just sit in the saddle, take your feet out of the stirrup and let them hang down. When they do this, your upper body shouldn't change much. Your legs can be positioned further under you with rolling more onto your crotch. If you were a posable doll, you could move the legs back without changing the position of the torso.
When you ride think of your heels as pointing back, toward the horse's back feet, and think of your weight going down , through your leg, PAST the stirrup and out your heel to meet the moving horse's back feet. This will liin you up nicely and make posting as bsms said it, "unfolding, and refolding, right over our the stirrup bars."