At the radiator shop I helped run in California for several years, we bought a special heat-conducting paint, and used the "spray the front edge" method to assure maximum heat transfer. Radiators work best with no paint at all on them, but most car owners don't like the ugly appearance of an unpainted copper radiator.
Different strokes for different folks- - - -if anybody else likes their way better, go for it. I've worked around enough successful professionals in the auto repair trade that I'm prone to do it their way. The guys who have to guarantee their work usually know what they're talking about.
Jerry
