This makes sense vs. the 'stack two pads together' instructions - thanks, all. NOW, if I can find a tool to reach the 1/2" nuts between the rear tire and fender! I tried to reach the nuts with a 1/2" drive and socket.. no luck. My hand is too big reach up there. Ugh.

 

The pads are needed so the plate mount does not vibrate and break. May of
these plate frames have cracked and broke because the pads were not applied.
The pads should be stacked and placed at the bottom centre of the plate frame.

 

A box end worked for me and the SGS is lowered 2" in the rear. Patience and safety glasses as its gonna rain dirt.

 

Like I said above, its all right there in the instruction, there's even a picture lol
From The Instructions:
5. See Figure 3. Place the 1.3 mm (½ in) bumper pads between the installed back plate and the rear fender bumper.
a. Clean the rear fender bumper with a mixture of 50 to 70% isopropyl alcohol and 30 to 50% distilled water. Allow to dry thoroughly.
b. Peel the backing from the bumper pad and apply to rear fender bumper. Stack the pads one on top of the other to achieve a tight fit.
Then there is a pic showing where to put the pad the picture shows the pads as round, but you got square ones....

there's also this note in there, same page:
NOTE:
Use the adhesive foam strips included in the kit to prevent vibration between the back plate and license plate.

I know I know... I get in a rush sometime too...
FWIW, when I added a curved tag base I found jacking the bike up and letting the tire hang gave me that extra bit of space I needed for my hand.

 

I think he’s right.