Tinker,
sounds fairly standard to guns I've owned or developed loads for, for other blokes, especially older guns that started life as black powder cartridges. I think is something to do with the differences in black powder and smokeless and while we can get fairly close with load development and trying different powders, sometimes the best way out is a taller front sight as you are suggesting, against the more costly re-regulating.
I bet there are no pressure signs with the Tolley tho!

cheers
Chris