23 mil / 2 = 11.5 mil of Up. Using 2 mil of the Up for the 100 yard zero and mounting slop seems reasonable. Leaves you with 9.5. Pop a 20 MOA base under it and you'll get 5.8 more mils, +/- mounting slop differences. If you really need the elevation, you could use a 30 MOA base, but your 100 yard zero will be edge of glass (image quality may suffer). If you're mainly shooting long range, however, when you do dial up you're moving into the middle of the glass.