Equation
Lieutenant General
The Syrian Air Force has taken a lot of losses. At the Start of the War, The Syrians maintained a distributed operation this was as they feared the Israeli Air force would destroy their Air force on the ground if they were all at one location.
Which is logical The Israelis did it before. But When they suddenly faced a conflict based around an Insurgency and rebellion all those small bases became harder to defend, a number were lost and adding to that now is the US strikes.
Russia could always them with used fighters and bombers on a needed bases.