M1602.2Return air openings. Return air openings for heating, ventilation

1.Openings shall not be located less than 10 feet (3048 mm) measured in any direction from an open combustion chamber or draft hood of another appliance located in the same room or space.

Being mindful of the above  (namely as  short changing combustion air can be deadly)  I was planning on cutting in a return vent on the FINISHED side of this wall. (see  red mark second pic) Because the rough-in is 4ft from my 40k BTU hot water heater, I wanted to double check on this. Again the return vent  will not be in the room the hot water is located, but the  duct will be running on the backside of the wall which is 4ft and directly across from the HW. 

I will foam around the opening when I rough in the return vent and also tape the  the finished side return vent to  the drywall to ensure I do NOT pull any air through the drywall considering the proximity to the hot water heater. All seams of the oval ductwork that will connect into my 6″ round pipe will be tapped. 

My furnace is direct vented sealed combustion, so don’t have a scenario where hot water heater and furnace competing for combustion air.  I do not have a fresh  air flexible combustion intake for the HW and the HW relies on the open air of the mechanical room