Thanks for trying Hannes!
I ran the numbers through a depth of field calculator and quickly realized my DoF-suggestion was impossible.
Given the MF's size I'd need a 200mm lens at 400m distance with an aperture size smaller than f/1 (>200mm aperture) to get a depth of field of less than 400 meters.
That should render the background mountain a little bit out of focus, but the lens would be a freak one and the viewer would not accept the image and say: this looks like a miniature.
So, you were right.