The main reason for the pin location for full rollers is to keep the flare from pulling the track over the thumb and/or finger holes.  The 3 3/8" distance sets the core at a 45 degree angle which gives maximum flare.  If your other balls aren't thumping the holes (or if the noise doesn't bother you) and you like their reaction, leave them alone.  There are a few other layouts that keep the track away from the holes, and the pin to grip center distance doesn't always have to be 3 3/8".  Ask your driller about it.  --  JohnP