1280x800 Scale 1 Portrait......... Works fine with 10" tablets and more importantly....makes sure it gets listed in the tablet section of Play Store.
Note that the variants have nothing to do with Play Store. This is a feature specific to B4A. (You do need to make sure that the UI is properly filling the screen.)
I recommend you to use the default variant (320x480, scale=1) and its landscape version instead of the first two variants you created.
The HTC Desire screen is equivalent to 360x533, scale = 1 (it is actually a bit smaller, especially in landscape). This is smaller than the smallest variant. In such cases the algorithm prefers variants where at least one of the dimensions fit.