GDP / Tax receipts cap

Is there a built-in cap for tax receipts getting boosted by GDP? I’m asking because I’ve been doing some modding and have noticed a couple of things:

  1. Raising the max GDP from 1 to >1 doesn’t seem to do much - it just sits there at 1. Eg if I want a crazy long game, once the GDP hits the cap… game over, basically.

  2. At such levels, GDP doesn’t seem to be able to boost tax revenues much.

For example, I’ve got an economy up & running that’s growing like no tomorrow. However, once it hits a certain point, it stops - if I want more tax income, I’ve got to raise taxes (either new or existing). So, any way I can work around this cap, or is this hardcoded?