Open space behind my studio setup


I need some help as for the acoustic treatment or positioning of myself in my music production studio. 

I live in a small 2 floor loft. I have set up my studio on the second floor next to my room where I have; two walls left and right, an one in front. The rear wall is about 12 feet away from my sitting position. The problem with the rear wall is; if I take 6 steps to my rear (from sitting position) I encounter a metal rail from which I can see down to the first floor. This means that 10 feet of space behind me is open space (bottom of rear wall is in the 1st floor and the top of rear wall is 2nd floor ceiling).

I have treated my front, left, and right walls with acoustic foam and 6 semi-quality bass traps on front wall, both frontal corners (3 traps each). My speakers are positioned around 1 feet from the front wall (I know it is not ideal), I am positioned 6 feet from my speakers in an equilateral triangle. Foam padding stops 9 feet from front wall (no padding or base traps in far rear wall). I managed to address the mid and high frequencies, but the low end is missing something, I can't feel the tightness of bass. Although, if I move 5 feet back (where the rail is) I can hear an overwhelming abundance in the low end which is not hearable from my sitting position.

I have not seen anyone online with a similar problem. Has anybody had a similar problem or a solution?

                      Front wall
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*Foaming ends here 
(Can feel intense low end in this area)
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               REAR WALL

aleco99
First, measure the response with REW, in your listening postition and elsewhere. Second decide whether you have a peak elsewhere or a null in your listening position. If it is a null, get multiple subs like the Audiokinesis Swarm system, or, if you want to spend less or have something smaller, get, for example, two SVS SB1000 subs.