Yes, that's where it has to be discussed. It could be an average or a virtual estimated maximum income, a border you could not cross.
We could set a maximum margin for each team, because so many factors can change the weekly income (cup games, merchandise, arena...).
Another way would be to set a salary roof for each division (1 million for div 1, 600k for div 2 or whatsoever).
But hey, it's not like a 1.5 million team (only the players!) like the venomous scorpions could ever make money with the current BB economics.
At the moment, it looks like the best accountants win, not the best global managers. We could give more credit to training and tactics that way.