> Merging an empty belt with any other belt, makes no difference.

I know the intended meaning was that it makes no difference to the result belt's type, but in-game it does have the important difference of putting all material from the input belt onto just 1 side of the output belt, halving throughput.

If in this image https://bartoszmilewski.files.wordpress.com/2020/11/unit.png the incoming belt had both sides filled, both would go onto only one side of the outgoing belt, possibly causing some stalling.

Do type systems exist that include a notion of "throughput" or "capacity" like this?