Rotating backwards was most likely the only way to reload the launchers, and also useful to quickly race away from the enemy after firing, but not sure if the backblast was damaging the superstructure too much this way.

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It's likely that firing sidewards was the typical procedure, like seen with the improvised ladders to climb on top to the vehicles. You can see some burning on the superstructure. Also check out the videos. They all fire sidewards.
https://www.youtube.com/watch?v=fMcVIfebarM
https://www.youtube.com/watch?v=LDgTDKPt_nM

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The unused
Armadillo_MkIII is the only ground vehicle in the game that also fires sidewards by the
broadside trait that normally only capital ships have.