I put Thiel CS3.7 floor stander into a 12 x 11 x 9 room. I needed to spend $700 to get acoustic treatments from GIK to make this work. I also needed to move reflective surfaces as far away from the speakers. I also do not have anything large in-between the speakers, just an amp. A bookshelf with books behind the speakers also helped.
Since I am a ROON user I was able to use DSP via professionally crafted CONVOLUTION filters. That can make almost ANY speaker work in my space. However, after rearranging the reflective items and adding 1 additional acoustic panel in front of my CD rack I was able to disable the CONVOLUTION filter. I think I am hearing the best possible sound in my room. A bigger room will get more out of the speaker but what I have now is satisfying.
Even though I no longer use the filter, the company that remotely did my DSP filter was this one.
They give you step-by-step instructions on how to measure your room using REW software and a mic. You give them the output files and they run that data through some very complicated software resulting in the DSP convolution files.