I think that if you worked on getting your lower leg more solidly underneath you it would greatly help the jumping ahead and laying on the neck. It all your photos, your stirrup leather is hanging behind the perpendicular. It's even the case in your flat work photo. It's not a dramatic amount, but it's certainly enough to create other problems in your form. In the photo on the palomino, you're also gripping with the back of you calf and rotating your toe out; this also shows up in slightly in the flat work photo, but is not present on the paint.
I don't want to take anything away from the fact that you're clearly a capable, athletic rider, but polishing up your form will take you to the next level.
Riding without stirrups is a great way to build your lower leg, and jumping low grids and gymnastics without stirrups is a great way to learn to wait for the horse and let him close your angles. On a flat work day, try securing the inside branch of your stirrup to your girth with a bit of baling twine or string. You'll be amazed what it feels like when your leg is truly underneath you. You'll also feel a tug on the stirrups when your lower leg pivots back.