A low altitude flight and dogfight with Mig-21 in close formation is a really tense thing. We have made several flights on the ACG Cold War Server. In the video you can watch a couple examples of teamwork between the leader and wingman: identification of an air target with following attacking and covering each other. It is very difficult to fight in tight formation because of the low altitude and high speed.
Low altitude flight and dogfight – in short of history
In the real world, flights and actions in jet aviation at low altitudes became a matter of interest since the Vietnam war. The US Air Force met an effective air defense, which used surface-to-air missiles and they lost many aircraft. At that time the USAF started training in Thailand where they found that airplanes were not adapted for flight at low and extremely low altitudes. At the same time, they found that pilots are not ready for those actions either. Even very experienced pilots became exhausted after 20 mins of low altitude flight 
Virtual flights vs reality
Modern flight simulators like DCS tend more and more to reflect real world aviation. As in the real world, flying at low altitude decreases detection by AWACS and also impedes detection by a fighter’s airborne interception radar. Additionally, low and extreme low altitude flying greatly reduces visual detection. In DCS virtual pilots, who used modern combat aircraft, decreased their flight altitude as an adaptation to the air defense threat. In the simulators there are no obligations or rules about altitude, it happened in a natural way.
In contrast to WWII aircraft, navigation at low altitude is provided by AWACS, ground control or by radionavigation instruments. In WWII flight simulators, flight at low altitude is complicated by the navigational needs. If you see online that WWII planes fly at very low altitudes, the server in most cases provides “magic GPS”.
In simulators of jet aircrafts, dogfight at low altitude are very tense because of the speed of the action. A bigger interval between leader and wingman provides for the best maneuvers, but at the same time there is increased the risk of losing each other. Small distance provides best visual contact between leader and wingman, but such flight even more tense. A shorter distance decreases the effectiveness of cover for each other.
On the video you can watch only two short fragments. Of course we lost each other a couple times. One time we rejoined over the airfield, another time ground control helped us to find each other.
Probably the best distance for low altitude flying it is the maximum distance at which the wingman can see his leader against the background of the earth and can follow him, and at the same time have an overview of the environment.
1 – Kirilov B. Flight formations in tactical aviation. Foreign military review. No 2, 1990. [Russian language]