Colin, Colin, Colin!
The nature of this little lamp is really starting to bug my gizzard!
When it is extended, the interior colour really stands out against all the exterior green paint, and it would be a fairly bright lamp in the dark when lit. All of that would logically seem to weight against its intention as a means of signaling, unless it was issued with some form of filter/shroud kit. Then, if it was issued with some form of kit, it appears the easiest way to install possible accessories would be in the extended position. In a combat situation, that could prove a very high risk task for the crew.
So I think about it a bit as being nothing more than an interior lamp. Seems over designed for that purpose, save for the rather restricted amount of interior room in the vehicle. The designers may then have decided for maintenance purposes, just make the lamp slide up above the vehicle. When done, slide it back down. That, however, raises (no pun) another issue: possibly preventing a lit lamp from accidentally being raised.
Do you have any wiring diagrams at hand that show the circuit for this lamp? At it’s simplest, I would expect to see an ON/OFF Switch located somewhere in series with the lamp. One could kick that basic circuit up a notch by inserting a spring loaded cutout switch in it to automatically shut the lamp off when it was raised for maintenance.
I notice in the last two photos you posted, an new little bit of metal work tucked into the lower bottom corner right below what is possibly the lamp handle support plate? That would be the perfect spot for locating a cutout switch for the lamp.
Then again, I could be totally out to lunch on all this...
David