Whilst the minimum width of the speaker is limited by the size of the bass unit, the sound in the room is not directly related to the driver's size. It is easier to design a smaller driver to be 'fast', and easier to get bass extension and higher maximum output from a larger one, which are factors the manufacturer balances. Of course, the Fact 8 has two bass drivers the same size as that of the 25-23, so has a total bass driver cone area equivalent to maybe a 7.5" or 8" speaker - about the same as in the 25-24.
I gather you don't like the Twenty5 24 in your room, so unless bass extension is lacking it would indeed seem a little unlikely that you'd get on with the 26, though it improves the midrange with a separate mid driver. However whether liking the 23 and not the 24 means you'd like the Fact 8 is another matter, though undoubtedly it is a step up from the 25-23.
You refer to the size of your room in a negative way, which I think is the small room (?) - have you tried the 25-23s in the bigger room?