I have to stress this:

DO NOT SIT IN SEAT WHILE MEASURING. DON'T TOUCH THE MICROPHONE.

Clamp it in headrest, in the middle where your head is normally. If you move the mic even an inch the measurement will be messed up. If you are aiming for repeatable results while correcting time coherency the mic must be absolutely stationary.

Elgrosso, The results you seeing on right side are probably due to destructive interference. I assume there's dips in the frequency response (AFR) at the same spots. Is this a 2 or 3-way? If it's a door mid it's perfectly normal. A small dedicated midrange should do better if placed optimally. Where is the crossovers?