tips for spraying primer

im using U Pol high build primer....what i have done to try to minimize the deepness of the pinholes is to block each panel with 255 until i start to have the paint underneath or bare metal showing through, then i stop...im doing this to as i said minimize the deepness of al the pinholes...before i reprime i will spray some self etch on the areas now exposed as metal...unfortunatly i dont really have any good pictures of the car right now showing its current state....ill try to take some tonight maybe and post them up...isnt the whole purpose of high build to fill in low spots and imperfections? thats what im assuming the pitting is, an imperfection, and that the high build will fill it...or am i wrong?