I have the same dual zone, 5 button Dometic Tstat but AquaHot instead of propane furnace plus a third zone on it's own Tstat and senor in the bathroom. During the day I adjust them much the same as at home... 74 in the summer and 68 during the winter. I just used my IR temp gun to compare the difference in indicated temp and actual. It's 1 degree warmer than the set temp of 74 and have never felt the need to check the difference before so I do not have your problem and do not know if it can be adjusted.
I would send a PM to
DougRainer as he knows these systems very well as a RV teck. He will know and willing shares his knowledge.