You cannot create different sizes for different slots/sites in the same layout. Its been requested but there are no immediate plans to allow that. I'm still not exactly sure what issue you are having with PokerStars. Can you show me some screenshots?
And if you are unhappy with the win10 gaps, you can use VisualizeGrid and just have the slots overlap a little bit. By default, SAT will 'snap' the slots to the edges of each other ,but if you hold down CTRL while you drag, that 'snap' will be turned off, and you can drag the slots to have some overlap so that the gaps you 'see' wont exist. Its likely thats what other software does.
And if you are unhappy with the win10 gaps, you can use VisualizeGrid and just have the slots overlap a little bit. By default, SAT will 'snap' the slots to the edges of each other ,but if you hold down CTRL while you drag, that 'snap' will be turned off, and you can drag the slots to have some overlap so that the gaps you 'see' wont exist. Its likely thats what other software does.