What he is trying to say is the bracket is much stronger if can spread the load along the edge of the box section and across the top face of it as well, you then weld effectively all six sides of the bracket. Just go on ebay buy some 7/16 UNF nuts drill an 11mm hole and weld it in place, a little tip grind the plating off the faces of the nuts first.
His brackets and mine look like this....
and I promised myself I was'nt going to post any thing today.