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

Miller so in a smaller room you cannot get good bass without subs ?

Correct. And small means small relative to wavelength. Since the the wavelengths of the lowest bass we want are 40 to 50 feet or more (depends how low you want to go) then small is anything less than that. Which means pretty much every room in every house is small. 

Look, its pure physics. Even at much shorter wavelengths we have to be clever with speaker placement and use things like diffusers and absorbers to get a nice smooth response. Exactly the same is true of bass, only the methods used have to be physically bigger on account of the physically longer wave lengths involved. 

Notice when you go to a concert in a large dome or hall the bass is wonderfully deep and uniform no matter where you go in the hall. That's because these spaces are large even relative to low bass waves. The waves have room to run and so when they do reflect off the walls its in different directions and times relative to the wave. 

In a normal room, say 20 ft, the leading edge of the wave bounces off the floor, ceiling, and all four walls even before one complete cycle! The darn thing is coming back and canceling itself sometimes right at the woofer! Think about it. 

But the flip side is if you take all this into account and do it right then you can actually have really fantastic bass even in a small room. You just have to abandon the old false paradigm of one or two subs and embrace the physical realities of long waves and use lots of subs. 

Because there's lots of subs they don't have to be big and powerful. Four or five ten inch subs is way better than one 20" even if the one is ten times as powerful. Because the one will create one powerful set of room modes. Bass will be thunderous but only at certain locations and frequencies. You will fight and struggle to tame this lumpy boomy awful bass. Which will not even go that low, by the way. But the four small subs will create four times as many different modes, each much smaller, so the bass will be smooth, powerful, and go really deep. 

DBA subs don't even have to match. Mine are a combination of three different subs. The bass is to die for.  https://systems.audiogon.com/systems/8367

@erik_squires: I only have a delay knob on my subs (PSA V1800). Is that what I should play with? I don't have polarity or phase controls.
@millercarbon Oh wow different subs? I thought I wouldn't be able to do that. Which subs do you have. Do you find they give you clean bass with your speakers and are fast enough to keep up?

Here are measurements during each sub off and then both on from the listening position:
www.diabolicaldesign.net/subs.jpg

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.

Lets say the diffusers, and traps and everything killed all the reflective problems, you have, what do you have left? 

Only what's coming from the baffle face, even the back side of a dipole would be killed.

So taking what MC said the wave lengths and killing the rest, you can only do a few things. Make a little bass everywhere, very even, very controlled, but everywhere. That's out, can't clutter the floor.

or You could EQ the bass, why? Your killing the reflective excess, so you can increase the actual bass in the seated position. BUT you can't kill all the reflective surfaces, so that's kinds out.

But the bass comes after the mids, and the tweets before the mids, so what do you do? You HAVE to move the speakers. NOT I can only move them this much, there is no other option. If you want to fix the problem..

The bass needs to be closer to you, the mids and highs need to be further away. TIMING.... they (lows mids and highs) need to arrive at your ears, at the same time.

Regards

Delay and phase in reference to a subwoofer are the same thing. Delay in this instance is the more accurate description of what the control is performing.

You have an unconventional listening space which may require an unconventional solution. Try what ever you can think of and see what happens. Aim your subs in different directions, Raise them off the floor, Raise them off the floor at different heights to each other, change the low pass filter setting (crossover point). There could be some cancelation caused by the interaction with the woofer in your mains. Try asymmetrical crossover points. If your speakers have ports try plugging and unplugging in various combinations. I'm sure there are other things you can try all you can do is see what happens.

In my system in a 14 x 10 x 9 room I have one sub sitting right next to the listening position aimed towards the main speakers and another sub almost directly behind that sub and aimed 90 degrees from it.

OP:
In general, your measurements show the two are not integrated. You want the bottom and upper part of this graph to merge completely seamlessly.

I only have a delay knob on my subs (PSA V1800). Is that what I should play with? I don't have polarity or phase controls.

My suggestion:

1. Minimize the phase setting.
2. Flip the wiring to the main speakers to compare.
3. Pick whichever wiring gives better response.
4. Adjust the phase dial from that point to eliminate null.
   
5. Adjust sub level to elimiate step between sub and mains.