Mobile variants are not supposed to scale and fit, it will display the closest matching variant to screen size ;)
Printable View
It seems to me that it picks the closest and scales that one so that either width or length touches a side.
So the cut off black square is puzzling me.
I just want it to fill the screen as best as possible for any given device out there regardless orientation.
I understand that this will probably be impossible.
The only reason I can think of that the black square is cut off is that Frank's Samsung wave's screen is narrower than your variant #1 and since that is the smallest variant thats the one that would be displayed ;)
The scale to fit option is only meant for short pages, as it scales to fit the entire page. So if you have a long mobile page and use the scale to fit it will render the page unreadable/unusable, and defeat the purpose of mobile variants. It is actualy intended for presentations where you need the full page visible.