The problem with using only %x and %y is that the text size is not modified, you need to change it too.
If you have SupportedOrientations = unspecified you need two layouts one for portrait and one for landscape.
The Scale module will scale the loaded layout.
I looked deeper into the problem with TabHost.
Unfortunately, the Scale module doesn't work with TabHost.
I don't know how to access the views in a TabHost, there is no simple way like with activities and panels.
Attached you find a workaround for the TabHost scaling.
The layouts for the tabs are on panels.
The panel height and width are reduced to take into account the tab height and the padding of the internal container.
This workaround is not perfect because the padding and tab height are not proportional on different screen sizes.
Using panels for the tab layouts allows to scale them with Scale.ScaleView for each panel.