I deal with a coupler of different variables when I make contact proof sheets, so I have developed a technique.
One of the variables is paper variation. From time to time people give me paper, or I find it in places like thrift stores. I use that paper for contact proof sheets (unless it turns out to be really nice, in which case it gets re-purposed). I use an Ilford EM-10 enlarging meter to set the enlarger light to my target intensity, and then do a test print to determine use my standard exposure for all of the rolls.
My darkroom is a temporary one, and the EM-10 helps take away some of the potential variability that arises from having to set up each time.
Another variable is light source. In normal times I also use the enlargers at my Darkroom Group when we have a meeting with lots of group darkroom time. The enlargers there vary, so I use the EM-10 there (if I remember to bring it with me) to set my target light intensity, and then go from there.
If I were Christopher, I wouldn't devote long periods of darkroom time to just doing contact proof sheets. I'd do a bunch, and then have some fun actually printing something each session.