Two Subwoofers... Comb Effect

I ditto the experience with sub(s) placed up near the front of the room, with the mains. Either multiple subs in one location, perhaps just off center on the front wall - near the center - , or similar, or subs near the mains, perhaps in stereo, maybe mono, depending.
It's almost always easier to get a better blend, even from multiple seating positions, and still maintain excellent cohesion from the subs to the mains, from the listing positions. It also eliminates any potential for hearing "voices" from your subs, overlap problems, and just plain integrates easier in my opinion.
While I think, carefully done and considered, you can build an excellent system around subs placed around the room, I think the benefits of doing subs up near the mains offers better integration and benefits - especially when you consider today's DSP and EQ technology applied!
Also, I don't personally like to see subwoofer sitting around the room. The gear is an "eye-soar" as it is, mostly. I'd rather be able to have the option to hide the mains and subs behind some facade if I so chose, in a custom set up. And this is all easily done with all the speakers up front, and side/rears hidden, somewhat. But, that's me.
Still, I can't argue with the excellent results I've had over the years with either one, or all of the main/front subs (usually rears crossed over to these subs also) up front. Clients have been ecstatic to!
Still, in each application, you likely will need to "tinker", and adjust for maximum results, and keep a balance.
Bottom line though, is the results is all that matters

If you have a steep-slope lowpass filter (24 dB per octave), then you can get away with spreading subs around the room. Most subs have a 12 dB per octave lowpass filter, and so will give away their presence and not blend well because they allow too much lower midrange energy to pass through. Since the ear localizes by arrival time as well as intensity, it makes sense to me that if the subs are passing audible lower midrange energy you'd either want them close to the mains, or farther away from your listening position than the mains, or both.

Since the low-pass driver is phase-lagging relative to the high-pass driver, I don't see any theoretical disadvantage in the bass region to having some of the subs a bit closer to the listening position than the main speakers - provided the above recommendation regarding crossover slope is observed. That really is a crucial aspect of a scattered multisub setup, in my opinion.

Duke

4 th order crossovers just never sound quite right to me despite the obvious theoretic advantages of 24db LR. Less overlap and summing to zero at the crossover as well as being able to crossover higher and not localize them. As a result I'm crossing over lower than I might otherwise. As far as the subs being a BIT closer or further away than the mains Duke is right in most real world situations but audible/non localizable frequencies ( 20hz-100hz) if they are in the crossover range will be arriving from two different sources at two different times. This of course may not make a pennies worth of difference in any given situation with any given listener - Jim

Most subs have a 12 dB per octave lowpass filter, and so will give away their presence and not blend well because they allow too much lower midrange energy to pass through.

That is what I have - 12 db/octave. That may explain why I prefer it up front.

Ok, points are definitely noted from those here responding about phase on the subs.
So here's some questions that even a novice might ask then. Which is, If phase doesn't matter on the subwoofers, in relations to each listner and the speakers, then why do subwoofers and even some processor offer phase adjustment in the first place? I mean, if you have one subwoower 3 feet from your listening position, and another 10 feet away, and maybe another 14 feet away from you, doesn't the phase get all confused and out of sync with the rest of your system?
I mean why does a full range speaker's woofer even have to be in phase with the rest of the drivers then? You mean it doesn't matter as long as you have relatively flat response from your sub-woofers, and proper volume level?
Maybe someone can address these questions concisely. Cause otherwise I think all the speaker engineers maybe put too much thought into making their large full range speakers so coherent in the first place. And not only that, but all the pre/pro's out there that have you specifying sub to listener position distance were just adding unnecessary steps to the process...