a 20X turnover rate in a 20 gallon tank is 400GPH. That is a LOT of flow, no need to point a ph directly at the acro. The purpose of a lot of flow is not so the corals "feels" anything, but rather that it gets access to more food particles and essential elements. That is why when you read that an acro needs a lot of flow, it doesn't mean the coral itself, but the entire tank. To keep acros, you should have a LOT of flow throughout your tank.
You have a 600, which is a 30X turnover rate. If that one powerhead can reach all parts of your aquarium, then you have high flow throughout, and the acro will suffice anywher in your tank (as far as flow goes). :happyfish