Im gonna take a guess and say the problem in this room is they are a dipole sending tons of energy (50% of its total output) on the wall behind the speakers. This energy is reflected back into the listening space with a delay that is created by the distance from the speaker to the wall behind them and then back again. This delayed HF is being added back to the non delayed main output from the front of the speaker all of it summed together at your ear. This is the same issue when we talk about first reflections: the same sound taking two different length paths to your ear is a sure way to mess up any speaker. Usually the top end is the most offensive as we are very senstive to this information. I bet if we measured phase in the room it would be severely messed up by this major reflection.
Dipoles are wonderful but very challenging -you need large spaces to make them sing. Id say this room is not right for a dipole. Nearly impossible to fix in too small a space sorry to say!
Brad
