Badger , sounds like you are lacking control over your air pressure, that would mean even if you get the right paint thinning sorted you will still get splatters due to highish air pressure. Maybe experiment with the screw in the can lid, tho i think what your missing is an air pressure regulater (auto shops} At 15psi you should not have splatters caused by air pressure. Also ( sorry to burden you) straining the paint thru a stocking will remove lumps helps! Gets me in trouble if I grab the nearest ones ( missus)