Another 3c Washington: Plating Help

I bought this on-cover stamp as a 10A, but I'm certain it is an 11A. Winston suggests it is a 1857 Claret from Plate 5L. I agree on the color, but am not sure about the plate.

It looks like an A-relief with no recuts beyond the inner frame lines. It also looks like a left margin stamp. I don't see any guide dots.

It does not look to be a good match for any of the left margin 5L positions.

Does anyone see anything that can help me narrow this down a bit?

It's actually a pretty tough stamp to plate. Perhaps the impression is a bit misleading? The alternative to Plate 5L is of course Plate 2L/3 but I didn't find a good match on my Chase photos. I mostly assumed Plate 5L because of the color. I see more pale clarets from Plate 5L than any other plate. The inner frame lines are strong enough so the stamp could indeed be from Plate 2L/3 rather than 5.

I've been wrong about identifying margin stamps before. . .is this one?