I couldn't resist a quarter round, 3/4 inch thick piece of plywood during my visit at Anderson International Trading in Anaheim. (Thanks Douglas S.) The piece was just waiting to be turned into a baffle The radius is 12 inch, giving a width edge to edge of 17 inches and a surface path of 18 3/4 inches. I mounted a RD75 after routing a slot in the quarter round. (Tip: a plunge router is not made to work on cylindrical surfaces, make a jig first ;-)
Some diffraction expected at 787 Hz which shows indeed up in the "standing" up plot. There seems to be "couch" support in the sitting down position as experienced during the listening sessions to music. Adding trapezoidal wings tangentially to the edges of the rounded baffle didn't change very much at all as compared to prior tests with flat rectangular baffles.
Above plot gives a different picture at 5 meter distance in the "sitting down" position. Couldn't find the matching standing up plot anymore ;-( I'll try to do a retake of this one soon.