Get the rifle low and keep it low. If your body position requires a sharp upward bend in the neck, raise the body by placing a firm pad under the chest. I tried this before I eventually had to pass on prone shooting. It worked to at least some degree. Our Club has a supply of quite firm surplus jeep seat cushion pads, about 16" square and about 2" thick, and that is what I tried. Keeping the support flat and parallel with the ground seems better (to me) than anything with some other configuration. My goal was to put the rifle and body in a better relationship, while avoiding any change in body position beyond relieving the crook in the neck.
Aside from adjusting to uneven ground, extending the bipod legs to shoot longer distances may be wishful thinking. The difference in the bore axis angle from 100yd to 1000yd is on average 30MOA for a rifle configured for LR. When we do the math, that corresponds to exactly 1/2 of one degree; hardly even noticeable, let alone worthy of bipod adjustment.
Greg