When having a hopper-cart or chest-cart running over the three hoppers as shown in the image, one hopper will receive twice as much of the given item as the other two combined. I discovered that 10/10 times, when the 3 hoppers are aligned west/east, the westmost hopper receives twice as much of the deposited item as the centre and eastmost hoppers combined. When the alignment is north/south, the southmost hopper receives twice as much of the deposited item as the centre and northmost hoppers combined. In both cases, the centre/east and centre/north hoppers receive equal amounts. I tested this many times, always getting the same result.