2 hours is quite a long time. You'd be better off with stronger dilutions, shorter developing times, more agitation, or some combination of the three. For starters you could shoot a low contrast scene at normal exposure, +2 stops, +4 stops, and +6 stops. Then give equal development to all sheets, say your normal time plus 20-30%, make prints all at the same paper grade compensating for variation in negative density with changes in exposure time. Then you could easily see the actual effects caused by changes to your initial exposure.
A great book that goes into medium to extended detail on this and other subjects is Bruce Barnbaum's, "Art of Photography" http://www.barnbaum.com/artofphotography.html. I have an older version (somewhere???) but I am sure the new revised version is excellent as well.
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