AWSD1.1:2010 Tables 5.9 and 5.10, Figure5.4(H)...
Does limitations of C (convexity) and R (reinforcement) not apply in figure 5.4(H) butt weld of unequal or different thicknesses? My personal opinion, the cap shouldn't excess 1/8". At the very least the cap or weld face should smoothly transition from one plane to the other plane, paragraph 5.24.3.