That may be why you don't hear a difference between QS10 and M5. Ears are less sensitive to noises from the back and even directly from the side. I have my QS10s forward. When I replace them with M5OW, the sound is more direct and the mids and highs are slightly more prominent.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated