Comparator does not detect any/single items travelling through the hopper depending on their setup. The way the hoppers are orientated DOES affect if any items are detected or not.

In the setup wth all the hoppers pointing to the side, none of the items are detected at all no matter the quantity. However in the setup with hoppers pointing downwards into eachother, placing one in the top results in the same thing happening but placing more than one item results in the items being detected.