I think you understand it correctly. There would be a post or ring at the front, and the rear of the tube would be deflected by vertical and lateral external adjustments.
The rear would have an aperture to aim through and possibly a corrective lens.
I have never used one, but a modern version used to be offered on .22 B.S.A. Martini International match rifles.
I assume that the tube was intended to eliminate varying light conditions from the side or above, but otherwise I can see little advantage over the more usual front short tube and aperture rear sight.
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