Thank you for the comment and especially for looking 'beyond the surface'.
It's not a bug. :-)
As with the PP, there is also a logarithmic formula behind it. That means for the first generators you get the underlying item almost 1:1 and to increase the growth rate you need more and more generators.
The formula behind it: (int)Math.Ceiling(1 + Math.Log(gd.Level[i],2));
I'm looking forward to your next post. And if you have time, I'd like you to be a beta tester for my next game. :-)