Most specifications call for the nominal bead diameter to be 50% max of the root radius. You state you are using AGB-10 which has a nominal diameter of .0039" You could use AGB-12 it's nominal diameter is .0047".
Another option would be to rotate the part around the lance. This way you could degrease your standoff distance. Is your lance a 45 degree or 90 degree? Using a 45 degree will also help increase the arc height but you will have to peen the part from both ends.
Hope that helps,
-Walter
