I experimented with the Brooks and different tilts. I can get my butt to stay where I plant it at several angles, but at those angles, my hands get numb from too much weight, and my crotch gets numb from too much tilt & weight. Still, I guess it's some sort of progress.
My bike is from 1973, the angles are 72 or 73 parallel. I just have a long torso for my height.
I find their seat-to-handlebar recommendations particularly problematic since there is such a wide variety of saddle lengths and shapes out there.
I agree absolutely, which is why I estimated my sit-bones to bar distance.
In any case, the numbers are for reference. My goals are to stop sliding forward, to minimize weight on my hands (which I think is mainly a conditioning issue), to not get my crotch numb, and to do these things on a low budget. (A lot to ask, I know.) IOW, making my bike match the CC calculator's output is not a goal. If the Brooks had 1-2 cm more adjustability, I think I'd achieve all the goals - since with the Aliante, which is 1-2 cm further back than the Brooks, my butt stays planted where I put it and weight comes off my arms.
27.0 is a known ID for Reynolds 531, IIRC. Neither the tube nor the seatpost looks at all deformed; the post is round, and it fits the tube very well.
I'll continue to experiment with tilt and I'll look for the SR seatpost, but right now I think my best choices are between 1) go back to slight uptilt and live with pushing myself back, in order to ride with no perineal numbness; 2) decide the Brooks is just not for me; 3) stay with the increased uptilt with no pushing myself backwards and just stand up frequently.
Thanks for your help. I wouldn't have thought of tilting the seat more on my own.