That is interesting issue.
From my experience the game is optimised well.
Usage of an office processor and low end graphics connected to super high resolution screen gives ... low performance. Surprisingly.
From your tests, the game scales very well depend the resolution.
Your hardware is suited for a Facebook user on a notebook screen resolution.
Compare one of my PCs is:>>> Core-duo and ATI 3870 <<<its about 10 years old machine. Its way below the official minimum but it gives me about 30fps on medium detais in 1920x1080.
I would recommend to install a new graphic card. 120-150$ will help you a lot.
Frames are definitely scaling with resolution, I just assumed that was normal.
800x600 on high settings I'm getting 52fps
640x480 on high settings I'm getting 60fps
