From my limited experience, I have found that it is not only helpful to be high, but also to be wide. I use 8' fence poles set on a 45 deg. Angle so with the beam of my boat there is about 18' between the pulleys. This reduces the chance of the line ever contacting other fishing gear in the boat. I estimate the pulleys are about 7' off the water.
Remember the higher your line the higher your lures will run.......