I've got threaded Delta Aztec brake pads in my Ultegra brakes on my
Cannondale road bike with (currently) Spinergy Spox wheels and
(previously) Mavic Open Pro/Ultegra wheelset.

The pads appear mounted correctly, in that the top of the pad meets
the top/outer diameter of the rim braking surface area exactly. But
the pads are about 2mm wider than the machined braking surface on the
wheels, meaning the bottom 2mm of pad doesn't contact the rim braking
surface.

So as the pads wear, a lip of un-worn-pad develops on the bottom of
the pad, and the lip rubs the inner/side portion of the rim. This has
worn away some of the stickers on the rim. I have to file down the
lip periodically.

Why would the pad be wider than the braking surface it mates with?
Does the lip contacting the inner portion of the rim during hard
braking present any problem? It seems like as the pad wears, the lip
would start contacting the rim before the rest of the pad, possibly
INSTEAD of the rest of the pad, dramatically decreasing braking power.