Should there really be that much difference between the length of the saddles?
IDK should, I'd Measure what IS.
Selle Anatomica has designed their saddle rails to slide back further than Brooks.
I have 2 Fizik Vitesse saddles one a batch shipped through Brompton Sales ,
allows a further setback than the regular ones , because of how the rails are bent,
and that was specified by the OEM customer.