Speaker size and soundstage

There are a couple of items for comment.  

First is room acoustics.  It's probably the most critical component in soundstage.  A well-tuned room is both the starting point and the finishing effort in any listening environment from the basement cave to the symphony hall.  Without the room, it will not be possible to set up a fully satisfying system.

A very easy and inexpensive room tuning solution is using 5" artificial ficus trees available at most home decor stores.  "At Home" stores sell them for $40 each.  I ended up with about 15 scattered around the room, mostly behind and next to the speakers.  They act as diffusers and work great.  It's probably the cheapest and most effective room tweak available.

Next is optimizing speaker setup.  Much as been written about speaker set up.  Most is total crep.  But do try to keep the speakers away from the back wall and the side walls.  Place an artificial ficus between the side wall and the speaker a little forward of the speaker to break up the sound heading for the side wall.  You don't want those side wall echoes.  

What is a "bigger speaker?" What is a "smaller speaker?"  

The Dynaudio Contour 30 is a VERY good speaker.  I haven't heard the Tekton.    

Soundstage and imaging can be somewhat controlled with the speaker setup and room acoustics.  Artificial ficus trees are the 

I have gotten spectacular soundstage and imaging using a speaker with a single 5" driver in a mass-loaded transmission line enclosure.  It was a nearfield setup in a larger room that the OP describes.  Wonderful system, punchy, tight and fun, but a little lacking in macro dynamic range and sub-80hz bass.  And nearfield listening helps to remove room interaction.

I get spectacular soundstage and imaging with my current 3.5 way four driver speakers with 12" and 10" woofers, 6" mid and 1" tweeter drivers in the same large room --- obviously NOT a nearfield listening setup.  But it does provide a very wide range of dynamics and sub-40hz bass at maybe 20 times or more the size of the 5" MLTL system.  

But the MOST satisfying listening comes ONLY in a room that is properly acoustically tuned.  

I got a fairly holographic presentation and deep bass with a standard version of the Salk Songtowers with at least half my LPs in my old 18' x 26' room. In my new place, they sound pretty good with better bass balance but not so magical.

It's about total system synergy and there's no way to tell until you get them into your room.

The size of the cabinet has more to do with efficiency than anything else. Given the same bass extension, a larger cabinet will require less power than a smaller one. That’s the trade off for low end - really big or really inefficient speakers. The size of the soundstage has more to do with dispersion and baffle effects and setup. Maybe someone has a link they can post to a useful video or paper by an actual expert. 

Forget either, and go out and buy some big azz Tannoys...you will get what you are looking for. My choice for you, the Ardens. Thank me later....although, I will point out that the cheap diamond 225's are a bit of a miracle little speaker...they produce an incredibly wide sound stage and produce copious amounts of bass for their size and price. I still own mine, despite now having tannoys....read about them in stereophile, $449 and a crazy good little speaker if on a budget. 

Sound stage has more to do with phasing, crossover points, driver dispersion, driver placement, and the shape and size of the front baffle than actual cabinet size. It’s also heavily influenced by placement, and the rest of the system.