I can't get proof anytime soon lol
However, I can tell the resolution definitely scales down because models and textures suddenly become blurrier and then goes back to crystal clear during gameplay.
I have to set adaptive resolution set to 50 every time I start up the game btw. It resets every time I start and restart the game.
What is your FPS and HW utilization when you notice these drops in image quality? Also game is far from crystal clear if you are running any of games AA options, or you are downsampling big time.
Edit: Developer set default value is 75