You may need to thin wall a wrenches box end.
In the last couple of decades I've noticed the walls of Craftsman level tools
getting thicker.
Seems the metal used is of lower quality so they have to use more of it.
You may need to not only thin the wall but also to reduce the boxes
thickness. I've had some box ends with a bevel inside the box that makes the
wrench pop off thin fasteners. Here it would just be getting in the way.
I know , hacking on tools goes against the grain. First time Dad torched I
wrench I thought he was nuts, damned thing would be useless for anythig
else. His response was, do I want that bolt tight? and sometimes you just
gotta do it.
Another thing that may help is to grind some height off the bolt head. Problem
with this is it could make it a real SOB to keep the wrench on.
If your go the 6 point route I suggest getting a close tolerance shim washer.
This will help in keeping the bolt head points from digging into the base metal.
Any way you do this, high temp Never-Seize the hell out of this.