Before I go and make a suggestion I thought I would ask here to make sure that I'm not wrong in what I think. At the moment when you resize a UWP window to the thinnest it will go it still acts as if it was full width of the screen. This is bad as when using the Idiom value in my layout it does not understand that the view is so thin, in this case the window has the same aspect ratio and physical size as a mobile.
Is there a way for Idiom to understand that while it may still be on a desktop, the app screen is not in fact the size of a desktop and more like a mobile. Alternatively a better solution would be for the view to have a flag that defines if the size of the view is like a mobile/tablet/desktop so that if you had a view on two pages, one where it takes up the whole page and one where it is more the size of mobile it could adapt to that size.