I have a furnace array with hoppers feeding fuel and items to smelt. Fuel and items are fed in by hopper minecarts running on top of the hoppers feeding the furnaces. They are at a different level and 1 block over. Weird thing is that the minecart running on top gets unloaded by the hopper minecart running diagonally below it.

The hoppers feeding the furnaces are facing the correct way. It seems that the hopper minecart can take items from a hopper minecart that is 1 block higher and 1 block over.

I took pictures of the two on my array, while putting a stack of cobble stone in the top hopper minecart. 51 of the cobble stone end up in the lower hopper minecart, 13 end up in the furnace.