Battle Economy Buildings Bonus

[Aitor-NationsLeague]

Hello all, this is something I have always wondered and can't really find on the wiki, is: How much is the bonus received in a battle for destroying all economy buildings of a given resource?

It seems to change and I haven't figured out the patron yet. Sometimes I receive 20k gold, sometimes 10k, what affects it? The age of opponent you face? The league you are? The stars you get in that battle?

I'm IA.
Thanks.

 

[Mythic]

opponent's age.
20 k, 150- oil; industrial.
10k EA, 50 oil