Duragrouch

Wow, that Nitto Campo lowrider really is low! I'd be less concerned about the mass location, and more concerned that the section aft would wag laterally about the relatively short span on the rack main verticals.

My folder frame (monobeam) is the early Dahon Speed so 4130 chrome moly steel, but it's plenty rigid, even in torsion when climbing with load, that main ovalized beam contains a large torsional section modulus. I've added an improvised "Deltech", but that stiffens it only in longitudinal bending, not torsion.

My rear pannier is just low enough to possibly affect rear derailleur function, except it's all behind the rear axle so doesn't (even though the derailleur switched from Dahon compact forward of the axle to conventional mount aft of the axle), and, is spaced out an inch at the lower mount because the rack is designed for discs (my bike has none, and I would have preferred the non-disc rack so no cantilevered load at the lower mount, but the disc version was all that was left, on clearance sale at Nashbar).

While high rear load (like my heavy trunk bag) might have a mass-damping effect for speed wobble, the pannier load being lower does reduce noticeably the rocking inertia when climbing out of the saddle, I have more leverage on it, especially critical if a long handlebar riser (mine is the old non-telescoping steel riser, so more rigid than the telescoping aluminum riser that was later).