I don't see how you can shift anything as studs are in the way. That return goes down how far -- is this first or second floor? Where is the HVAC? And why is there a gap in your return air duct? Something is not right here.
Its the third floor and the HVAC is in the basement, though the return doesn't appear to be lined up on any of the floors – not sure that they should be or you were asking.
The gap looks more like general laziness than anything else, as if they didn't want to cut the cardboard bit to fit around the stud. I don't really know much beyond that, sorry. Hopefully someone still has some thoughts or suggestions.
