I agree with Phishook, although you may not be able to do that the first time you work on the hedge. In any case, your goal should be at least vertical if you're not able to taper from bottom to top. We always instruct our people to taper everything they cut with hedge shears. The problem with pruning too much at the bottom is that you start to loose lower limbs because they shade out, then you have even fewer lower limbs to work with.