There is. The is a correlation between the CURRENT total leadership of your army and the CURRENT total leadership of the enemy army. If the enemy has higher current leadership, the XP gained from dragon abilities will increase and vice versa. If your level is higher than the dragon's, the XP gained will increase, and again, vice versa. There is also a modifier based on killed enemy troops.
Besides, the numbers that were used in this calculation are the ones found in the game files and formulas, so they must be accurate, unless the game has decided to cheat you somehow
