I’m looking to be able to set the minimum tab size to something lower than the default 20 width, since I’m editing more than 5 files at the same time. I’m using the Productivity Power Tools extension as well.
You can right click on the space beside the tabs, click Customize...

and then Advanced Options then edit the value from there, but it doesn’t allow you to go below the inital size of 20.

Is there a configuration file somewhere I can edit to solve this, or is there an obvious solution that I’m missing?
The solution actually was the maximum size rather than the minimum size. So just tweaking the maximum size value was what I wanted. Not ideal, but still, the answer.