+1 on pstake's reply.
Long development times with high dilutions (a favorite is 1:100, from 20 minutes and up depending on agitation schemes - stand, semi-stand, etc) yield acutance effects.
The smaller the format size, the more they are seen in the print.
You can find more on this forum by searching for "stand" and "semi-stand", many threads gone over the dam.
One more question. What is the difference between "stand" and "semi-stand," or is it the same thing?