Android Question Tablet resolution

Did you try 1.4 as the scale factor?
Anyway, I generally use only the sandard variant with anchors and some scripting.

I think that you would agree that most developers are trying to design a layout that will look attractive on as wide a range of device resolutions as possible. The Layout Designer has been developed to meet this requirement. Using it to design a layout for a single, very specific, screen resolution, as you are, means that you are fighting against this design ethic.

There are many posts on this forum about designing for specific variants and the answers tend to have one suggestion in common - don't use variants. As @udg implies, even if you set up a 1200x2000 variant you will probably get easier results by using anchors than by trying to calculate the width and height of every individual view.

Variants can be useful when designing portrait and landscape alternatives, such as "top-and-bottom" and "side-by-side" layouts, and sometimes when having two different layout styles for small and large screens. I think that those are the only situations where they should be used.

As for the dark grey area, it is a mystery to me too. Don't worry about it.

The Tab A7 display is WUXGA+, so it will max out at 1920 x 1280