One instance is the tradition Ibn Abbas narrates from the Prophet (a.s): [Arabic omitted] The prayer of one, who doesn’t put his nose on the same thing as he puts his forehead, would not be accepted. -- Al Islam
So it looks like we should place our noses on turbah too. However, some of the stones I've seen are very small, too small to reach from one's forehead to the tip of their nose. This puzzles me.
Question: Are both your nose and forehead supposed to rest on the turbah during sujood?