Hopper can't pick up items which sit on top of the stand of a brewing stand

The range at which hopper can pick up items from is inconsistent, because as far as I have tested they are able to pick up items which sit on top of a block which has a hit box as high as 0.875 blocks (soul sand) which is placed on top of a hopper.
However hoppers are not able to pick up items which sit on top of the hit-box of the stand of a brewing stand which is placed on top of the hopper (which is only 0.125 blocks high).