Hi C.N.,
Perhaps this tanker skipper was wiser and more experienced than the convoy commodore. With a highly explosive cargo aboard, it just might have been self-preservation to drop astern of the convoy at nights.
Many collisions occurrred when steaming in tight formations without position lights. A collision with this cargo aboard would have the same results as a torp hit.
Also the wolfpacks used to tear into the convoys at night, thus trailing them astern is arguably safer than being in the middle.
Rgds, RB