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#11
Actually Windows 10 appears to be using a 'Fill' algorithm, your smallest dimension is the width, which has been scaled to fiil the available width of the preview.
I have copied your image and used it to recreate your folder in Windows 8.1. This appears to use a 'Fit' algorithm. The largest dimension (the height) has been scaled to fit the preview. I'm not sure how (or if) The W10 behavior can be modified to match that of W8.1.
These terms FIT or FILL are used by Microsoft for othe image scaling, such as for the desktop wall paper, so they are likely to be the relevant terms to search for, either on the web on in the Registry.