Looking at the game-specific drawings (specifically GE-09032), it appears that the outpost base is 24" deep with a square pattern of mounting holes starting 3.5" from the back that might be associated with the seat.
From the picture (thanks, Elgin), it looks like the seat back ends up flush with the back of the base plate and the payload specialist is basically sitting at floor level plus an inch or two, but I can't find any drawings of the chair to see where the mounting holes match up
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