On my upstairs shower and bath, both p-traps will be draining into a 2" horz line....which is only going to be about 12" below the drain of the respective device....This is about as far down as I can go until I transition down another wall into my main sewer.
So....I assume that there is no min height? I hope there isn't.
I do know that the vent for each respective drain has to be at least 6" aove the highest drain connection (that part is not an issue)
Even if you are on the right track, you will still get run over if you just sit there.