your only trying to fracture the paint , not pit the metal. i use 35 lbs pressure and stay off the panel 2 ft and use very little media. but my rig is much larger. starblast is a very good media. very fine and will recycle about 4 times .
when blasting concentrate on peeling the edge of the paint back . blast at the edge at an angle not straight down.
i use type6 acrylic to remove paint .