He doesn't specifically mention the 850 GS, but it's the same as the 1100 (or the 850R if you prefer)
The system cases are moulded to fit snug to the bike, so have a very inconsistent shape inside. To use all the available volume, socks, knicks & other small items always have to be packed into the same nooks & crannies each time, to leave the unobstructed space for larger items.