Really depends on a few things, what magnification you like to run and how sensitive the eye box on your scope is. In the mag range I generally run (11-16x and 25x for zeroing) I have my scope placed so that I have good eye relief in all position, be it prone or positional with it possibly set to slightly favour prone, as that is where I would conceivably use higher magnification. On a good scope (I use Leupold Mk5 5-25s) the eye box shouldn't be all that finicky when not running at either extreme (ie I run a 5-25 between 11-16). I also run an ACC and just have the butt stock collapsed as short as it will go as that gives me an ideal LOP for being squared up. You'll notice a finicky eye box more on a 1-8 or another LPVO, especially when going from shooting standing squared up at 1x to kneeling supported or prone at 8x.