Counter-heroes in duel mode (3.1).

By the way, I noticed something a while ago related to the "education" skill of duel heroes. My Letos had a varying amount of mana – sometimes 60 (as in the manual), sometimes 75, and sometimes 90. Anwen had between 40 and 70, and Jalib also fluctuated, but it wasn't that significant – 160 or 170. I think it's obvious that the amount of mana, say, for Letos, seriously affects the battle tactics. So, the question is: is this a bug, or was it designed this way to make the game more interesting? If it's the latter, then it speaks well of Nival :)