POP paper, slower emulsions,less aggressive developers, etc. etc.
Preflashing does reduce the contrast as well as increases the effective speed of the paper.
Originally Posted by Fragomeni
Measures like these and others that people take to combat the challenges of paper negs escape me sometimes. Paper negatives have been used successfully since the beginning of photography and it was never as complicated as people make it out to be (myself included). I've never found pre-flashing to be useful or serve any real purpose. Paper is orthochromatic, treat it as such and use the methods devised 150 years ago to efficiently capture an image on this type of material and it should work in the same ways it always has.