Tourist, nice info. I really could not see the logic of a narrow top platform on rear rack, I have a trunk bag. But now I see that on a long tour, it may be better to bring the panniers closer and use a big top bag like you have. I think my rack lower tiers are just high enough for the panniers to support a big bag, but have most of the weight on the rack, and not pushing down on the panniers.
Gosh, touring with a trailer and LWB 'bent was so much easier in loading, but that was a bear just transporting in a car, and that's with a folding-frame recumbent; Via air or even train, that would be near impossible. And can't even wheel or carry up stairs. And hill-climbing was terrible.