Open Floor Plan Listening Room

I have two recommendations to make. The first is to go for at least two smaller subwoofers instead of one big sub. In most situations that produces a far more even response. See here for some reading: http://www.acousticfrontiers.com/20101029using-multiple-subwoofers-to-improve-bass-the-welti-devanti...
The second suggestion is to invest in a DSpeaker Antimode 8033 room equalization unit as well. This tightens the response significantly in both the frequency and time domain. With two subs this is even more effective because the equalization will be effective over a larger listening area. Subs have a bad reputation in audiophile circles, but this is largely due to the problem of the room modes that they excite. These not only produce peaks and dips, but they also linger on. People speak of slow subs, but it is not the subs that are slow, but the lingering room modes.

Excellent, thank you.  Funny you should mention Acoustic Frontiers.  That’s who I reached out to for a quote in order to handle the work of calibrating and positioning my subs and speakers.  They are local to me so if the consultation price is right that’ll work out really well.

You might be sitting in a NULL spot. I use the 1/3 speaker setup and have used the 1/5 setup in the past. This means placing the speakers 1/3 of the room length from the rear wall and my listening position is also 1/3 from the wall behind. Since you are hearing a lot of bass 45 ft away, I would try using different speakers and listening positions in your room. Check out speaker room setup from the likes of Cardas and others

an open floor plan shouldn't really have a null spot

But what if it does? The description seems to be exactly a null, which could indeed be the case if the listening position is halfway the length of the room. But it could be that the louder bass elsewhere is actually a peak. So as I said at the beginning, measurement should come first. The only investment is that of a $75 calibrated measurement microphone.