is there a goal behind that instead making a narower tower (else than putting the cabinets on shelves near a wall) ?
I'm not sure I understand your question, but a narrow tower can't have much directivity. It takes horizontal physical dimensions on the order of a wavelength to have horizontal directivity at a given frequency. (Not counting dipoles or the like, that is, which get directivity via a backwave).
An overall goal of the speakers is to make them look as small as I can. Wife doesn't want, in our small living-room, the monster-size boxes or panels I would otherwise tend to make!