Images of areas appear blurry

I have a problem with the areas in my world In my specific case I use 2 areas as a background image for my world. The 2 images i use have the same scale (in px) and file size. However one appears blurry while the other appears sharp in F&F. The one which appears sharp has less details as the one which appears blurry so I suppose F&F downscales images at a certain point. But at which point?

I am confused since the two images are identical referring to file size and resolution.

Any fix for that?