KingOfSnake:
In my view room size is an issue with Beolab 5's, they sound congested and do not perform in smaller environments (Beolab 9's are far superior in most setups where I have placed Beolab 5's). Many years ago I tried them in a 8m long room, 3m wide, they were very average.
Twice I have collected Beolab 5's from customers who use with Beolab 2 subwoofers in smaller rooms. The first time I thought it was a joke, the second time I began to look into it further. The auto-calibration dampens the bass output in smaller environments, so much so that the advice I was given prior to (re)installation was to use an extension lead, take them out into the garden and calibrate them outside!
The above may be technically flawed but from someone who listens to Beolab 5's in varying room sizes, all i can say that is Beolab 5's need a larger environment to perform well, in my experience they are suffocated in smaller rooms.
I've got to quibble with parts of this, noting that KingOfSnake is absolutely entitled to his opinion and preferences. Characterizations such as "they sound congested" and "Beolab 9s are far superior in most setups . . ." always make me extremely uncomfortable in the absence of the scientific underpinning of appropriate test and measurement. Such characterizations are, of necessity, anecdotal opinions and I get unhappy when they are instead presented as close to general fact. Sorry about that, but it makes me cringe.
The B&O development team (especially Jan Abildgaard Pedersen) worked quite hard to get the ABC to work reliably and consistently in a great range of rooms. There was some serious science there, with exhaustive test & measurement, listening evaluation and endless discussions about "what do you mean by the right amount of bass?"
Calibrating the BeoLab 5s outdoors (in a free field, essentially) will cause them to increase their bass output. It seems to me that such an outcome is what you actually prefer to our measured "flat response." Your preference for the Beolab 9 suggests the same, because it was voiced to have a substantial bottom end, which I enjoy plenty but often feel is just a bit much.
Keep in mind, the Beolab 9 has basically a "single response" solution while the Beolab 5 has an "infinite adaptation to power response" solution. The appropriate way to change the voicing of the Beolab 5, should you not like its realization of "flat," is through the use of a good equalizer. Interestingly, I have experimented with a number of EQ tweaks for just this reason. Never adopted any of them permanently.
So, returning to room size: I can think of no physical reason for the Beolab 5 to be constrained by a small room. I have mixed with them in some VERY small rooms, and found them extremely easy to use. One of the things I adore about them is their room-to-room consistency (a result of manufacturing consistency that is to closer tolerances than any other speaker manufactured, the ABC, and ALT).
As I said at the outset, you are absolutely entitled to your opinions and preferences. I do have qualms about your science, with all due respect.
Best regards,