It's unique it looks cool and some times even I like to add a bit of form to my function
But if you want a technical reason okay, you see that part at the back of the turret that's where the crew is and so they have an extra peice of armor between them and instant death should an energy weapon strike there, we are talking afteral about energy weapons that would likely chew through even heavy armor in short order so let's say Leons like to have that extra layer AWAY from the crew so that when it gets vaporized the guys in the turret it's self may have a chance to go "WHOAH" and run away thus saving their lives
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