I too use a Hobart Handler and like it a lot. I do set my flow meter to 30 cfm. I find I get a little cleaner weld with the higher setting. How about taking some scrap metal and set your flow meter higher then work your way down and see at what point it begins to deteriorate. When you trim the wire you allow the purge gas to displace the oxygen before the arc is struck also. One last thought. How clean is the bottom side of the metal. Could you be getting some contamination from the underside of the panel.