I've seen cases where the EOR allowed only the flat portions of the joint and ignored the corners(TS radius).
However, If it were done in my shop, I would like to see one of the following:
-A continuous 1/4x1 flat bar bent and fitted around the inside of the 45* beveled TS16x6x1/4(be sure to full pen the joint in the backing bar so that it is continuous), leaving 1/4" outside to give you a 1/4" root opening.
-A 1/2" or thicker plate cut and ground to fit snuggly 1/4"(depending on plate thickness used) up inside the 45* beveled TS12x6x1/4 leaving a 1/4" root opening.