The location you should is probably the worst possible place for deep bass. The fact that you have to crank it up so high and that you are hearing a lot of port noise is evidence of this.
Is the opposite corner (top-left in the picture) available? I'm thinking that's likely to be best for place for both mid bass and deep bass.
Another reason the mid bass may be weak is because of poor integration with the mains. One thing you can try that might yield immediate improvement is toggling of the phase switch. Another possible adjustment is the subwoofer distance, but this can be hard to set by ear. What kind of mains speakers are you using?
A room measurement system can be helpful here. You can also use an SPL meter and test tones, but this is much more tedious to do and doesn't give as much insight unless you take measurements at a lot of different frequencies.
Under most circumstances, Audyssey should improve the in-room sound quality from the sub, but it sometimes gets confused. It also doesn't take into account the crossover between the sub and mains at all. I'd suggest giving it another try once you have a better idea of what's going on with your mid-bass without it.