A very small amount of matcha powder in chocolate milk makes it taste 10x better. You want to heat it to boiling in a very small amount of water in the microwave to extract the flavor. Normally, you don't want to overheat matcha otherwise it will be bitter. But that's what we want. What makes chocolate good is that it is a bit bitter. Otherwise we'd prefer plain sugar. So even a small amount of over extracted matcha will make the flavor pop.

One of the reasons to use a very small amount of water is you don't want to heat your chocolate milk. So I'm talking about entire drops of water. If you don't like it then you used too much. Somewhere just above not being able to taste it is chocolate milk that finally peaks to a full satisfaction of flavor.