Mountain Bike Vs Road Bike Seat Height. I find my mountain seat is slightly lower than road. While those two methods may seem very similar, they do sometimes seem to result in seat heights that aren't equally as comfortable.
Riding a bike that doesn't accurately fit your frame can lead to injury. Mountain biking takes your cycling routine off-road, where stable terrain and smooth inclines rarely appear. Your wheel axle height sets your bottom bracket height..
Since it is your road bike seat height that feels "off", if it were me, I would initially set my road/tri seat height to be the same as my MTB seat.
While those two methods may seem very similar, they do sometimes seem to result in seat heights that aren't equally as comfortable.
Stand over height is the clearance between the top tube and the bottom of your crotch. Adjusting your saddle height is a good excuse to clean your seatpost. See a professional fitter if the problem.