I have read the replies & all I can say is if what your riding feels good & works for you & you ride many miles injury free then it is all good.
But for all the comparisons to seat tube angles relating to TT etc I will just say "for myself" again
setback has absolutely nothing to do with reach
(in my experience)
Setback as I see it is strictly the distance I am sitting behind (in my case) the BB. This allows my legs injury free pedaling in all situations & RPM's
Of course we all probably also move a bit on the saddle for different situations but.......
That aside I am not going to get my setback requirement on a steep STA period. I ride a 73 STA with a 25mm setback post & am pretty slammed back at that. For the curious my setback is 8.57cm
That is tip of saddle nose BEHIND BB center on a saddle that is 275mm long
So STA is important to me personally & IMHO is the most important fit factor as it cannot as I said previously be fixed with a longer or shorter TT or stem
Again these are all in my opinion & is what has worked for me
EDIT: I see now too that
Dave's post also pretty much said the same as what I think