I've found that with SMP's (the best saddle shape for mirroring the pelvic bones btw) tilt correlates pretty directly with riding position. I have my SMP's tilted slightly nose up since my riding positions aren't all that aggressive and that's just how my pelvis is rotated when riding those positions. If I were to lower my bars significantly I'd also need to tilt the saddle down.

With flat saddles having the saddle level is a good starting point. I'd be more suspicious of nose down rather than nose up since that would indicate that the saddle shape is wrong or the nose is too narrow. Ideally the saddle shape should be such that when rotating the pelvis forward, the saddle and nose should support the pubic rami pretty far up the saddle. If there's only one sweet spot which allows for no nose contact, the shape isn't good.