I know what you mean. Bear Studios' MiG-15 and MiG-17 are both the same way. LOTS of fun to fly, but not much time in the air. The MiG-21MF (or any other MiG-21) never has had long legs, being a very fast point-defense interceptor. A couple of them (at least) were lost over North Viet Nam because the American pilots engaging them ran them out of gas. That was why ground-controlled-intercept (GCI) was so important to the North Vietnamese Air Force - they didn't have much time at all to loiter or be looking for American aircraft - it was essential to be steered to a favorable intercept point for one quick attack, then a break-away - or else to be quickly steered to a sanctuary airfield in southern China. Having an interest in old Soviet technology, I've followed the MiG-21's story for a while - it's an attractive airplane. I've downloaded it, but haven't flown it yet. If you're a little short of gas after what seems to be not much time in the air, then it sounds like the aircraft's modeling is pretty accurate.
There was a two-seat training variant of the MiG-21 as well. Maybe if we're lucky that will eventually be modeled as part of the series. The Soviets almost always built two-seat training variants of their fighters for instructional purposes. If you think this model of the -21 has short legs, consider this - the -21 trainer's second cockpit took up the space normally (at least partially) occupied by one of the aircraft's fuel tanks, giving it even less range than the single-seat variant. Makes you wonder how much you can learn with such a short training flight. The learning curve in the Soviet Air Force must have been steep indeed!