Thanks Jorun,
If I do some work on Ruellia hydroponically, I shall report back.
I find Ruellia get rather leggy and ungainly. As well as cutting them back harder to keep this trait in check (hopefully), I think I will try rooting cuttings on their sides (laying them in a tray of water) - so, once planted in soil, new shoots will start from ground level. Well, it's just an idea...
Mike