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


I guess this is relatively common in listening system. Is there any way to smooth this out so I get more bass energy at my listening position? This happens with our without my 2x 18 inch subs. Room is 12 x 16 x 8 ft, speakers 4.5 ft apart on long axis and I am sitting 4.5 feet away. I tried moving back and forward but the entire middle center of the room except near the walls has decreased bass.
Is this a boundary effect or could it be due to bass cancellation effects?
smodtactical
Move you listening position closer to a wall boundary.  You may need to be anywhere from inches to 2-3 feet from the wall.
Guys thanks for all the feedback!
I forgot to mention my speakers are Yamaha NS5000 and they are about 1 foot off the wall. As for the separation I know its not ideal but i just don't have much space because I have a door to the left of my left channel and my sub to the right of the right channel.

My right sub is at the front right corner. My left is at the back left corner. Both firing down the long axis. I guess if I had 4 smaller subs I might get a better response than 2 subs. I don't have a ton of space to move my subs around because of other items in the room.

Would changing the firing direction of the subs make a difference since bass waves below 80 as you said are non-directional. I might be able to move one of my subs to a position where it is to the right of the listening position firing at the center of the room. I can't really do a crawl again because of so many other things in my room (it is a bedroom).
And I guess I am kind of stuck with the bass without subs because to fix it there I would have to I am guessing pull my speakers out further which I can't do right now.
I wonder if diffusers behind my speakers would help? In addition to bass traps. Because I can't pull my speakers out further than a foot off the front wall.