FN - if the nose is tipped down it might make your pelvis roll forward, placing your weight on the soft bits and nose more than their fair share, and making you feel like you are sliding forward.
Even when the saddle is slippery (and it does get better with repeated applications of proofhide) you shouldn't feel like you are sliding or falling forward all the time.
Tip the nose up a bit more (a SMALL amout at a time) so your pelvis and weight roll backward more toward your tailbone than your soft bits.
Did we already have the pelvis-as-a-bowl-of-water discussion?
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson