I sight in at 9X (highest). Then verify at 6X and 3X (lowest). I do this when i first purchase the scope and again just before hunting season although i shoot year round.
I have several Nikon Prostaff's and there has never been a change to impact point at any magnification.
Early on i had some very inexpensive Bushnell's ($45). They also had the same impact point throughout the entire magnification range.