Flat front trousers shouldn't be high rise. Fullness and rise correspond. Pleated pants usually have a higher rise so that the fullness can be distributed effectively over prominent abdomen/thighs. You can't achieve this with flat fronts unless you build them with darts under the waist band. I do this when I remove pleats from pants for myself. I keep a small dart there so some fullness is maintained.
RTW companies like Jos A Bank etc make flat front trousers with high rise to fit more people, but it's why you see droopy crotches because no one wears them that high. The alteration, by the way, is dropping the waistband. And you've got about an 1.25" before you start cutting off the pocket. The higher end RTW companies drop the rise on flat fronts because they know that the pants will inevitably end up at the hips like jeans, anyway.