What films are you using and how are you processing them?
If you had a film you liked in MF and then moved up to LF with the same film and developer, but processed MF in daylight tanks and LF in trays with constant agitation, your sheet film development time could be considerably shorter than your rollfilm development time.
I suspect something along these lines is part of the issue, because the difference between a condenser enlarger and diffusion enlarger is not likely to be as great as the difference you are describing.