There is a setting which allows players to get 1 army for each e.g. 3 territory earned. However, it would be cool to be able to set negative values so players who are getting bigger will lose some income.

A mod already exist, if I remember right

There is indeed https://www.warzone.com/Mods/Mod?ID=388 that implements this.

If you would like it in the base game, you should make a feature request for it because Fizzer will ignore everything else.

True, the problem is that mods and mega games don't work yet.

I will contact Fizzer