I finally had a chance to follow my instincts and try the right side, since I was having problems with the left. Now, remember, for me, this was on an F800R, so the screws appear to be the opposite of the pictures.
Here's the drill as I figured it out:
With the bags on the bike, first remove the screws located fore and aft that connect the outer protective "ribs" to the fabric covered lids.
"Close" the lids, but allow the ribs to fold down. Now you have access to the screws shown in the OP's pictures. These are easily accessed at the bottom; just lift the fabric part up. There will be four in the recess on one side, three on the other, with the fourth being inside the bag. Once you have those screws out, "open" the lid again, and lower the combination of the lid and the ribs. The combined weight should cause the flat bottom piece to move down from the inner shell. That piece fits into a groove in the back of the inner shell. If it all doesn't fall off, you may need to push inboard a little to disengage the two halves.
If it still doesn't come apart (which the left one did not for me), this may be the problem: The U-channel "mount" that engages the tubular pannier support on the bike may have been adjusted such that the flat piece can't move inboard and come off the inner shell. Loosen the two T-30 screws inside the bag and wiggle the mount, and you should get the two apart. This step may need to be done with the bag off the bike.
Now, the metal "hoop" that supports the fabric half is held into the hinge at the bottom center by a loop that engages tabs in the hinge. To get that loop loose from the hinge so that you can take the fabric half apart from the ribs, take the bag, turn it upside down in your lap. Now, if you rotate the flat piece that engaged the inner half, you'll see the point at which there is the least interference with the metal loop. With it in that positon, push the hoop toward the hinge. It will come free, and you can maneuver it around the retainer and off.