So there are obviously various opinions floating around on the best arrangement. Here are my results...
Room: 13 x 16, with 2 openings in one of the short walls (the original back wall)
Before arrangement: Speakers on the short wall, 8 feet apart, pointing toward the back wall with the openings, about 2 feet out from front wall and around 2 feet in from the sides, toed in for near field listening, with axes crossing just in front of the listener about 8 feet from the base of the triangle. This arrangement sounded very very good...
After arrangement:

Wall with openings is now to the right. Speakers are still around 8 feet apart, now a little less than a foot from the front wall, listener still about 8 feet away, but the axes are now crossing behind the listener, who is a little over a foot from the back wall, which are mostly taken up by large windows. (Blinds can be pulled.)
This arrangement sounds...better! See, I had tried this kind of thing with my previous speakers, which were Revel F30s, in a different room of the same width, and it just didn't work. Maybe I didn't do it right, maybe those speakers were too big.
It's hard to describe the difference between the before and after setups. Kinda like the difference between listening to players on a stage and actually being on the stage with them. This setup has really taken the room out of the equation. I had been worried that I'd be sitting too near the back wall (reflections). Even with minimal absorption behind me this does not appear to be an issue. I had been worried that I would sacrifice some imaging with my equipment rack in between the speakers (before I could keep it in a closet out of the way behind). The imaging is in fact even better the new way. I was worried the proximity to the front wall would mean sacrificing some stage depth. Nope. I'm just sitting on the stage and kinda surrounded by sound. And the bass is, of course, pleasingly reinforced this way. A subwoofer might theoretically improve things, with difficulty, but it definitely
is not necessary. You don't believe me come over and hear for yourself!

The bass really does fill the room quite well.

So it sounds...like you might expect it to sound with more air on either side of the speakers. High frequencies are given more room to breathe, there is more a sense of space (which was not exactly lacking before), and everything just
gels. The bit about "pressurizing both halves of the room equally" must be accurate. As for the center image...I just don't understand how good speakers do this!!! I can't hear a centrally placed soloist emanating from the speakers themselves no matter how hard I concentrate. It just sounds like my rack is producing the sound. PAY NO ATTENTION TO THE LITTLE BOXES ON EITHER SIDE OF THE STEREO RACK. Spoooky.
In short, this is the arrangement I will be sticking with. I recommend anyone try it who hasn't and can. (It also makes things look nicer having everything out in the room...I also can't believe I recently contemplated, in a moment of weakness, trying out a different speaker, "for fun." Well, also because a floorstander would be more child proof...But when you get your room basically out of the way, these 1801s are keepers. The system just sounds complete as is, thank you Dave Ellis.)
And thanks again for all the input people!