Hi Leif,
For discussion purposes....
I don't dislike the shape that Dom is making his backs. But, I still like the idea of flattening just the heel end so the sides are parallel. I think it could be done so it wouldn't look objectionable when the saw is fully assembled. I plan to use his backs. I will attempt to flatten that area as you suggested an individual can do.
I understand the concern about stamping one's name on the side of the back and deforming it. A lot of people who will make a saw or two probably won't bother with stamping their name on it. Those who make lots of saws can accomplish it in other ways. If one were to stamp their name on the back you modified, it could still deform.
I've said this many times before. At the risk of being repetitious about something that few, if any, are in agreement with or interested in, a traditional mortised handle is basically a poor design. When the handle is screwed only to the blade, the handle can flex from side to side. When the mortise is made to fit snug to the back and the handle is flexed side to side, the flexing creates stress to the wood around the mortised area and cracks or breaks can occur. If the teeth are maintained sharp at all times, it is not as much of a problem as when the saw becomes dull and the user continues to use it. Most of the repairs I have made on old backsaws were made in the mortised area. All of those old saws had bad to horrible teeth. Owners of those saws actually tried to use those saws that would no doubt jamb in the kerf. I know there are other ways damage can occur, but if the mounting of the handle to the back and blade was solid, there would be less chance of cracks.
Here's my point... if a mortise is used in the traditional way, it would be best to have at least one screw through the back (Harvey Peace?) along with at least two more through the blade. When the handle is screwed to the back, it would be best to have a back with parallel sides, so the clamping of the screw would be even and effective. This is one reason I prefer a slotted back. There doesn't seem to be an all-out objection to slotted backs, even though they are non-traditional. But, no one wants to improve the problems surrounding the use of a mortise made in the traditional way.
If it's tradition that some people want, the saw should be made exactly like the old saws were made. On the other hand, if we are going to change one aspect of the design that is non-traditional, why not other aspects of the design?
Making anything strictly for traditional reasons doesn't seem practical to me. At least one saw maker agrees with me on that point. Veritas. They stepped way outside the proverbial box on their backsaw designs. I applaud them for that. No mortise on those saws.