That is a big miss isn't it. Especially when you are .5 MOA at 730 yards! I have a 25-06 with a 4.5-14 scope that is always about 6. MOA at 400/500 yards. I shoot both prone and off the hood of the truck when the grass is too high. I can hit milk jugs at 400 and steel at 500 all afternoon from prone or off the hood. I have not noticed much change in point of impact either way.
Off the hood, I usually lean my chest into/onto the hood using a 6 inch bipod. I spread my elbows and place my left fist into my right arm pit. I rest the butt on the fist and use the thumb to raise lower the butt. Use the same method a lot prone too.
I have not noticed much bounce difference with the bipod off the ground verses the hood of the truck. Maybe your ammo was bad or had something to do with the way your were stabilizing the butt of the rifle. Something was way off though to miss the whole deer at 400 yard with a .5 MOA rifle! Some experimentation would be the only way to know for sure.