I would guess that the nearfield extends about 10 or 12 feet from a line source speaker, whereas it extends about 5 or 6 feet from a point source speaker. This is strictly a SWAG (so correct me, Jim!).

Anyway Marlboro, I would still want to diffuse or (if necessary) absorb the first sidewall reflections, as they are the ones most likely to be detrimental to imaging. The floor and ceiling bounce are usually the reflections most likely to cause tonal coloration, but the directional properties of a line source take them out of the picture.

Something else a line source gives you - a wider sweet spot. The loudness discrepancy between the two speakers is less for off-axis listeners, so you get good soundstaging across a wider listening area.

Just my $.02.

Duke