For me it's a fine line. I have an Adamo Race and too much downward tilt and I find myself sliding forward. But if I put it perfectly level then the nose of the saddle puts too much pressure. But there's a narrow range in between where I'm actually comfortable: with just an ever so slight downward tilt.

And I'm most comfortable on the bike when I'm working hard. On slower rides I find the tri bike rather annoying.