Correct. In order for the FD to work correctly, it is mounted the exact same place on a frame. And with that fixed location, a FD can interfere with the rear tire if it gets big enough. So a frame should really have 2 max tire sizes, 1X & 2X......and of course for 700 or 650....so even though a frame may say it can accept a 700x48mm tire, 2X and using a FD may only allow a 40mm tire on that same frame depending on the FD being used (the tire will hit the FD before it hits the frame). I know Di2 is tighter than most mechanicals. From what I understand the GRX FD was slimmed down a bit to allow a few more mm tire clearance - maybe 42 instead of 40? I am sure SRAM did something similar. Going 1X now removes the FD entirely so tire restriction now goes back to the frames restriction.