Thanks Harold. I think I follow? The issue is the possibility of the rear tire hitting the pinch bolt? I thought it had to do with the frame geometry or something else along those lines.
Stupid question...doesn't chainline refer to the ability for smooth shifting across wide-ranged gears? If so, how does that impact the tire clearance? Just learning as I go, here.
I mean, the issue is a combination of things. Some frame geometries won't allow the FD's pinch bolt to swing through it's entire range of motion without hitting the tire if the rear wheel is really tucked up to the seat tube. My frame allows plenty of room, even with tires near the maximum size that'll fit in the frame.
Chainline does a few things. And what you mention is ONE of those things, especially when dealing with a 1x drivetrain. There's a narrow range of optimal positions for a 1x drivetrain to be able to effectively reach the low and high range of a modern cassette without problems.
It impacts tire clearance on the narrow end of chainlines, and when you're pushing tire size as large as you can. This is why fatbikes have such enormous chainlines. It's primarily a tire capacity reason, so the chain can clear the tire. With gravel bikes, there's an interesting bit of history involved.
Road bike hub spacing was settled at 130mm for a long time. When road bikes started getting disc brakes, they started to move to 135/142mm mtb hub spacing. When that happened at the hub side of things, crankset chainline didn't change. On the whole, it wasn't a problem because it was only a couple mm, and that's generally within the narrow window for smooth shifting across a wide range 1x cassette.
With gravel bikes pushing the tire capacity side of things, now there are starting to be issues. Not on all gravel bikes. But some. Shimano figured it made sense to shift the chainline out 2.5mm to line it back up with where the chainline was on 130mm spaced road bikes. This helps the chain to avoid rubbing on the side of the tire when in the lowest gear. They also changed the pivots on the GRX FD to avoid interference problems with bikes that had rear tires tucked up to the seat tube. That became an issue for the older type front derailleurs because to reach the wider chainline, you have to pull that arm the pinch bolt is on lower than you do with a narrower chainline, which brings it closer to the tire. The arm on this FD is a pretty clear example of something with the potential to interfere with the tire.
This video shows that using a road FD is possible, but his example road FD is a newer one with a similar function as the GRX FD, so it doesn't have the same tire clearance concerns that the one in the pic above would have.
This is the FD I'm going to be using. It's an older 105 FD. The arm the pinch bolt is on isn't as long as the Ultegra I posted above, but I have clearance for days between the frame and the tire. I think the cage can handle a chainline a couple mm wider than what I have now.

0125211425 by
Nate, on Flickr