Minecart Hoppers do not correctly disperse items

When stacking hopper minecarts on top of each other with or without a block separating each layer of minecarts they appear to exhibit some variance of favoritism in the distribution of their items. To my understanding, using the item input and hopper configuration shown in each example should evenly distribute the items into each container, which they evidently do not as shown by the lamps I used for an easier visualization for where the items ended up.