My feeling is that creating a 10ms delay between the sound from the rear of planars and that from their front is the first priority. Anything less than about 10ms, and the rear wave is not perceived as ambiance, but rather as part of the direct sound---a smearing of it. Our ear/brain requires a 10ms separation between two sounds to recognize them as separate events.
Since sound travels at approximately 1’ per ms, to create that 10ms delay between the sound from the front of a planar and that from it’s rear reaching the listeners ears, the planars need to be no less than 5’ in front of the wall behind them. It takes the rear wave 5ms to reach that wall, and 5ms to return to the planar. It then continues on to the listener, who perceives the 10ms delayed rear wave sound as ambiance, rather than part of the direct sound, as a smearing of it.
In a 14’ room, with the planars 5’ out in the room and 8’ from the listening position, that leaves 1’ between the lp and the wall behind it. Unfortunate, but the lesser of two evils; that is, if one makes the 10ms delay the first priority. Absorption on the wall behind the lp is then required to prevent reflections off making the wall’s presence known to the ear/brain. Also unfortunate is the fact that there is undoubtedly a room node located right where the lp then is.