I do the same trip each day in UB (well, really, each evening). I call a taxi and a metered taxi arrives at the apartment and waits for me to come out. There is no waiting charge in Mongolia. All metered fares are distance only.
So, I have been taking a taxi each night now for a couple of months. Over that period the taxis and I have travelled exactly the same route. The metered fare has ranged from MNT 4,500 to MNT 9,000 each trip. I know that the MNT 9,000 fare was dodgy as at the half way point the driver’s meter was showing MNT 2,600.