Jay, Welcome to the forum,
I will say that if the print calls for a single pass 1/4" fillet and your welders are putting 3 passes to get a 1/2" fillet, your welders are costing you money.
I'm not certain that you could get a single pass 1/2" fillet (except with SAW in the 1F position) and still be able to adhere to the acceptable weld profiles in Figure 5.4 of the D1.1:2002.
If you find a statement that does not allow what you are asking about, please post it so we'll know about it and can share with others.
John Wright