I have a split level home. The central return WAS located about midway down the hall between the bedrooms and steps that lead up to this level. Hallway Closet are the doors on the right. See old pic below:

It was in a bad location for 2 reasons. The first was that when the grill was on, the pull was so strong that it would close bedroom doors that were part way closed. Second, the current location of the attic steps required one to climb over the return trunk when ever you needed to service the unit or access other parts of the attic. Takeoffs on the plenum, to the bedrooms, were bent to get around the height of the return. Thus, I decided to swap the steps with the original return location, so that you come up right next to the AC Unit, making it nice and easy to service.

Below are two pics showing the new steps in the center of the upstairs hall and in the one pic you can see the older steps, still located on the ceiling to the left (To be removed shortly). Question is, where is the better place to install a new central return? Figure size would be the same 20x30 but don't think it needed to be as deep as the current return box. I am thinking like 8-12" deep max. Would have a 16" round 90 degree elbow off the top connecting to the Flex Duct return.

I am thinking possibly:

1) Install the return in the old stairs area. Would start closest to the main hallway side. But the 30" dimension would run the same long dimension as the old stairs do now (Left side). This would mean that the grill openings would face the lower level to pull air up. Drawback is you could see into the return from downstairs, when in the hallway looking up the steps. This would put the return around the corner from the bedrooms but there is a bathroom to the left.

2) Install the return in this same area but turned 180 degrees to that the long 30" dimension runs the direction of the narrower side of the old attic steps on the left side. The grill would face the main hallway and would pull air from up the steps and probably the hallway. This would hide the visibility into the return from downstairs but would still be visible in certain spots.

3) Frame and cutout a new opening centered roughly where the smoke detector is hanging down. This is closer to the top of the landing and would be in line with the old steps but over the center hall area. The grill could face in either direction (to the bedrooms or towards the stairs. visibility into the return would be the least visible here. If the grill faces back to the bedrooms, I am not sure if it will have the same suction or not but since its further down the hall and has open space to the left now vs, being in the narrow hall, it would probably have less of a pull.

Are any of these good options? The old return was 20x30 but was very deep, like around 24-30" high. Is that depth really needed or can I go with something more like 10-12" or less so that the whole area can be embedded in cellulose? I'm sure most of my heat loss was through this return as well as heat gain in the summer, when AC not running.