Minecraft wiki entry for Hopper, associated text: Setup: When initializing such a sorter array any "oh3-B" filter-hopper ("F") can only be be filled with filter & filler items after at least one neighboring "oh3-A" has already been initialized. The "oh3-B" comparators need the neighboring comparators to output at least a power level of one to keep their own filter+filler items from flowing out too.
Overflow: When a "oh3-A" sorter row/tile overflows it disables/locks the two neighboring "oh3-B" sorters. They can still pull up to 62 items from the hopper transfer pipe but they won't be able to put those items into each corresponding storage until the overflow situation is fixed.
The stone slabs can be replaced with normal solid blocks.
A total redstone delay of 4 in each sorter row/tile ensures that the filtering hopper's comparator stays at the activation level while it's working and doesn't flip between active and inactive. In other words: The output-hopper ("O") doesn't pull items from the filter-hopper until the later one is ready to pull a next item from the hopper pipe above (thus keeping a stable amount of 2+1 filter/to-be-sorted items in the filter-hopper). This reduces lag(?).