I’m having trouble wrapping my mind around the idea that extra girth makes length gains more difficult. If you make gains with lig stretches, then that doesn’t seem to have anything to do with girth. If the “cord” is your limiting factor, then girth gains shouldn’t affect that. If you are stretching the tunica, that seems possibly related, until we realize there are two layers of tunica - transverse and longitudinal - and one restricts girth while the other restricts length.
I know it seems sensible to think of an overall thicker unit as being more difficult to stretch, but when you break the penis down into its component parts, it becomes clear that length and girth work target different areas.