hmmm wow...the absolute best tinters will bring it to 1mm but not less because then you substantially risk it getting caught and ripping off tint or causing issues over time from that, so if you don't even see a 1mm or even slightly less, than wow I'm perplexed.
If it's not tint, you sure it's not some weird dirt like small water marks that over time have really stained the windows? Maybe take some really strong cleaner and try ti get it off...maybe it will just wipe right off. I bet this is it because listen to this:
A few months ago I noticed that my headlights in some places were tinted and other areas not so much and had a ragged edge. I was absolutely convinced that my tint or the black paint was peeling from the inside of the headlights (the FX50 has darkened headlights/tailights). I took it to the dealer and they confirmed it. When I got the FX50 back they said the mechanic took a look and was convinced that it wasn't actually tint peeling or anything and had the car detailer have a wack at it. So the detailer buffed the headlights and they came out brand new....they actually got those spots off.
After thinking about it longer, I had put rain-x on the headlights, waxed it, and wiped it off. I bet the rain-x eventually caused that! I tried everything in my life to clean the headlights and it didn't come off that is why I was convinced, but then they buffed it and it came out like new. You may be having a similar issue!