There is DL scaling and legacy scaling. Legacy scaling uses full-fledged target resolution, while DL scaling uses some shenanigans to help with performance. What you're seeing for 8K and 16K is 4K legacy scaling with supersampling from the game on top of it which results in true 8K and 16K resolutions. So, 4K x 2 = 8K; 4K x 4 = 16K.