Too thick? Add a little more milk when you respin. Don't forget the respin step - it's important. Because this mix is high in protein it needs the respin plus milk to hydrate well.
Too soft? Use less milk during the respin or freeze longer. Be sure to freeze the full 24 hours. It makes a difference.
Different milks behave differently, so start with 10–12 oz and adjust as needed.
TIP: Prior to spinning: Let the pint sit out for ~30 minutes or run it under hot water for ~30 seconds to loosen up the bottom and edges. You don't have to do this but it usually helps (especially with the chocolate).