Bigger drivers = bigger soundstage

"...The larger driver speakers do not image as well..."

Your post obfuscates at minimum.  We have no clue unless you tell what you are running. 

The larger the driver the worse the dispersion. That's basic acoustics. Only way to change that is with acoustics lenses.

Then again you have two different rooms so the discussion has hit its end.

" The larger the driver the worse the dispersion."    

The larger the driver the NARROWER the dispersion.  Narrow dispersion can be better, it depends on the application.  

Duke

Agreed Duke, thank you for clarifying what I wrote.

In terms of size yes, but the question is WHY the larger driver sounds better. "Saturation" is the best term (for me to understand). The larger drivers are quicker to beam in comparison to their smaller counterpart. That part being a higher frequency driver.

EX: 3 way, front fire. TMB arrangement, rear port Box speaker

IF the XOs design accommodate the drivers, properly and the sensitivity of the drivers is CLOSE (very close <5%). The larger driver is gonna out gun the smaller drivers.. It is as simple as that.. This is from the Speaker box as a complete assembly.

I’m not accounting for a room in any way, only from the actual box and it’s components.

I’ve built speakers and learned, "pick your drivers well". What does that mean? Woofers are woofers.. They work well where the test well. Just because a manufacture claims a driver works from 20 hz to 600 hz
doesn’t make it work well within THEIR test parameters (they lie a LOT). It is ALWAYS dependent on the crossover points with the parameters of a PHYSICAL driver size. 6 - 12" drivers have limitations because of physical size, It doesn’t matter how far you move a cone beaming will occur because of physical size.

Upper and LOWER limits. Don't push 5" drivers to 20hz it's not gonna happen.. Don't push 12" drivers to 2500 hz it physically does not work well.

Today a LOT of the newer speaker drivers are pushed beyond what a physical driver of that size can do because of "BEAMING". Yet because of DEEP throw (HE) drivers, we see it all the time. That is where the dispersion effect falls short. I call it saturation depletion, exacerbated by poorly designed, and untreated room surfaces.

In other words, bigger is better if it’s designed correctly. Every step BACKWARDS, from that position in a simple box speaker, diminishes it’s ability to out perform is SMALLER brother (sister). Apples for apples.

That’s just my long winded BUT simple way of saying WHY..

Large two way speakers, don’t get me going....:-)

I can get all teckie if you want LOL

Regards