1) You have to acknowledge that vertical velocity is measured by how much the center of mass is displaced, not your foot.
If I understand right, you are describing the flight time, which should be a PRODUCT, not a cause, of the amount of force applied in the ground. Only way you can change it, is by changing the force applied.
2) The shorter your legs get during the gait cycle (the more folded they are), the less your muscles have to work. Laws of physics are working for you, there’s no need to lenghten the legs. You’re felling more sore in the hip flexors, well, because you are working them harder. You can have your heel coming to your bum and then let that momentum transfer to the knee lift, and consequently the hip flexors won’t have to lift the thigh as much, laws of physics are just working for u.
I think you should make a video 🙂