I can give it a shot but the photo is lousy:
The first thing is that my rack is considerably longer than stock, so it not only projects more at the back of the bike but it projects forward toward the saddle also. It is in the front projection where I added two more screws by drilling holes right through the grab bars and using screws and nuts (technically I guess they were bolts and nuts but I digress....).
There is a well where the rack is supposed to mount to the bike (Easy Ted!). In front of that well, the grab rails get thicker so where my rack projects, it must be thinned on the bottom to fit. You might be able to (barely) see the milled areas under the rack where I relieved it to fit all the way down into the original rack wells. This is no doubt why Givi chose to use external 'outriggers' to provide additional support to their -55 mount; there is just nothing that can really be done with the stock bike otherwise to really increase the strength of either the rack or the grab rails where the rack mounts.
Again, the thing is that this rack is thicker but also quite a bit longer than a stock rack; the front was lengthened to add those to additional fasteners as the stock screw locations are so close together. A Givi 55 is a big box (Boys!) to begin with, and while I would never do so, I have heard that <some> people overload even those things (I have had trouble carrying that top box into hotel rooms
). Given that, I would just not trust the original four screws to fasten the box, even with the thicker plate. Please bear in mind that the grab rails are not aluminum as they appear to be but are in fact plastic, though a very strong plastic but still.... With the larger rack shown, along with the additional screws, I calculated over 1,000 lbs. of force required to deform it (not actually have it outright fail) although of course I do not know the strength of the grab rails in the first place.
Brian
I agree. Brian can you give some insight on the holes you added?
Also in previous note you said; By the way, the bottom of that plate is not flat; it must be stepped or cut at an angle to lay flat on the forward grab rails. If left flat, it will not seat in the well provided for the luggage rack.
Are you saying the flat bottomed Aluminum plates (that are comercially available) are not correct as they are flat bottomed?
Ride safe, Ted