My own experience is that I need the nose down about 10mm to prevent numbness. I base my setup on Steve Hogg, Colby Pearce, and especially the patent application, which is IMO essential reading for anyone interested in Selle SMP. The patent app is available here, for example: BICYCLE SADDLE - SELLE SMP S.A.S. DI MAURIZIO SCHIAVON

Albcici (Selle SMP in the US) says their saddles are usable with tilts of +10mm/-25mm, although they suggest starting with the saddle level.

Hogg is very informative about Selle SMPs. He says that most of the SMPs are designed to be ridden at varying degrees of nose down. A Colby Pearce asserts 'The nose angle should be set as low as possible, provided the rider is stable....' (SMP Setup Tips - Pearce Coaching and Fitting) Pearce goes into some detail on that point, and I recommend reading his words on SMPs, too.

But this is a question of comfort on a bike which makes the assumption that the saddle is the element that needs to be gotten right. The assumption itself may be invalid.

We can't predict what saddle will suit specific people. I'll agree there's a correct setup for Selle SMPs for each individual who uses one. I can't agree there's ONE correct setup (as in 'the correct setup'), and I can't agree that the Selle SMP will be liked by all riders.