I always run out of slots in and outside of my FC house because I love to decorate, everything needs to look clean, especially around the holidays.

A fix would be adding even more slots but I don't think SE would want that so why not just make that number shared so it won't put more stress on the server. That way if your new layout happens to run out of slots outside or inside.. you can just "move them over" (sacrifice a bit outside for inside or the other way around). This basically means that all slots both inside and outside would be counted as 1 number/amount.