Scopes mounted low help minimize canting error. If a scope is too high it increases the problems associated with scope cant, when the reticle is not plumb. This causes the POI being further off the longer the target distance, a problem potentially compounded by wind. In long distance shooting, if the scope is perfectly set up, that is without being "off level" or out-of-plumb, accuracy is unaffected by how high the scope is mounted. When both the rifle and scope are canted accuracy is again compromised as target distance increases. At shorter shooting distances there is a measurable difference when scopes are mounted higher.
If the scope is mounted plumb, that is the scope axis and bore axis are aligned, the most important thing is that it is comfortable to look through the scope when it is mounted on the rifle. There is an aesthetic appeal of a scope mounted low, but not all rifles have the same height combs. Easy eye-to-scope alignment is key.
