The big thing with front der limit screws that are at their limits is that the der's swing and resulting cage position, WRT the rings, can be at the limits of working relationships. As the frt der cage goes through it's swing it moves both in and out (which the limit screws directly control) and also moves up and down. So the gaps between the cage's bottom edges (or the various sculpting of the cage plates) will raise and drop as the cage moves in and out. When the cage's side to side movement is at one end of it's travel (as when the rings are far from the frame) this vertical component of the cage swing is greater, conversely when the cage moves through it's inward portion the vertical component is usually less.

This results in a non linier response to lever travel and cage/chain displacement. Changing the ring's distance from the frame can affect the der's ability to shift. But this too has limits. Andy.