What he is saying is that you put a wedge - probably a bit of old inner tube (free from any bicycle shop) - under the leading edge of the Mudsling, where it mates with the frame. It does not have to be very big, which is why you do not have to remove (just losen) the two screws and can leave the rear cable tie in place, or you will end up juggling, screws, two bits of rubber, cable ties and a Mudsling. A task that you are possibly ill designed for, not being an octopus.
The wedge will push the Mudsling away from the frame by a few mm at one end which, lifting the 'southern' end away from the bolt.
In short, you are trying (and achieving) to create a gap at the 'southern' end.
All will become clear. The rubber will not be unsightly. Indeed, if you cut it properly, it will be hidden within the natural curvature of the Mudsling.
Total time? 30 minutes. Job done.