Yep, the liner in front of the tyre. My wheels could come in 20x11.5 18mm or 20x12 25mm. I did a test fit with the tyres on the stock 20x10.5 19mm wheels and that convinced me I couldn't do 20x12 25mm.
In fact it was so tight I actually grabbed a piece of paper when the car was up on the ramp and ran it past this pinch point.
I'm actually going to swap them back onto the car soon, probably Monday or Tuesday next week depending on how busy I am. I'll try and take pics of this point when it is up on the ramp.
https://www.6post.com/forums/showthread.php?t=1677487