I've also used the Paterson 2- and 3-roll tanks, for about 25 years, usually with 2 or 3 rolls. There has never been any apparent difference in negative density.(posted 9307 days ago)I agitate by inverting the tank, about 1 inversion per second. Continuous for the first 30 seconds, then 5s per 30s.
In theory, 2 rolls in a 2-roll tank will get different agitation, because there is a small air gap at the top of the tank. Inverting the tank will partially uncover the bottom film, but the top one will be permanently immersed. I don't know which film would then get the most agitation, and as I say, I can't see any difference.
Robert: has this only happened once, or is it consistent?