I also use a very small listening room. In my room, with two REL T5i’s the soundfield and extension is slightly better than with my speakers by themselves. The key I think, is to make sure you are not impacting the mains..
if the mains sound better without the sub, this is a sign that the sub is probably running too high in the mix, IME.
if the mains sound better without the sub, this is a sign that the sub is probably running too high in the mix, IME.