Lots of bass at walls, lack of bass in center of room/listening position

Bass nodes.
All you need is 2 more subs and hours to spend setting them up.

http://arqen.com/acoustics-101/speaker-placement-boundary-interference/Hrmmm
No more space right now for more subs

I have a single 12” sub in an open ended approx 15x25 room.  My first location produced bass 20’ away but very little in the listening area.  Moving the sub only a foot and a half, close to a wall ( 4”) and experimenting with forward and side firing (into a corner worked best)  produced smooth response in the listening area.  The sub is across the room from the main speakers (Wireless helped here).  Placement next to the mains seems intuitive but may be just the wrong thing for your room nodes and it’s not necessary if the crossover is set properly.  Good luck!

Your speakers are 4.5 foot apart and your 4.5 feet from the speakers?
That is close to you and close together. WOW!

You are in the wrong place and so are the speakers, it sound like, a bit of humor.  Your in the "cancel zone", if the bass was trapped you would have bass, its the bass bouncing from everywhere to the center (where your at) that's the problem. Cheapest solution move your position.

Correct solution, treat the room as much as you can, place your speakers further from you and wider, get yourself a lot closer to the actual, bass bins, either side of you, or forward of the main speakers, it's a timing issue. Either kill the unused bass or get rid of it, (open the doors on the back wall if you have them). Then you can hear the bass in phase, (correct timing).

Regards