I downsized a couple of years ago and moved my beloved B&W 802 from a large room to a regular bedroom in a townhouse, about a third of the space.
I was thinking I would need to sell them and get small monitors but decided to keep them. I've got two big bass traps behind the speakers and additional room treatment. It sounds a lot better than what I expected. It is true you may not be able to have enough space for the drivers to fully integrate, but I don't think this is so critical, at least not in my setup.