The rear guard loop looks small, but works as advertised.
Another way to visualize it is to (mostly) center up the bike with a piece of 2 X 6 under the kickstand, then slide a piece of plywood up to the rear tire and lift up the other end until it hits the guard. It won't touch the bag.
Of course in a low-side slide, ideally you want to tuck in tight on the bike, hold on and let the bike take the hit(s). Easier said than done. I dumped my IS in the dealer lot on a brand new greasy (release agent) front tire, at about 3-4mph, and it went down so fast/hard it flung me off like a rag doll, and I slid backwards on my back, farther than the bike slid. I had simply forgotten I had a new tire put on 15 minutes earlier.

Injury to pride was worse than bruise to hip. Bottom of guards scraped was the
only damage. I scrub all release agent off new tires (delivered to house) with bleach and hot soapy water and a stiff bristle brush forever after.
Do stupid stuff, win stupid prizes.