It's a matter of increments.
The TRB above is better than some of the earlier TRBs, but could in fact get the tailpieces a little bit closer to the end of the bass; there is room for a little bit of shift (though small). The upper horn doesn't quite reach the 12th fret; it's in between the 12th and 13th. The ideal is probably sitting between the 11th and 12th, though very few basses do this. (And I happen to find those necks a little wide, as well as the string spacing not quite being narrow enough.)
All the little things add up to where the 35 inches of scale ends up sitting, and how far over to the left it is shifted. At least in my experience. I guess my reach is just a little bit shorter than others.