My son also throws a circle change. Good point on the "million grips". We experimented with several before he found one that kills velocity, has some movement, and some sinking action. It took a good year to find the right grip and get comfortable throwing it. Several pitches in the dirt and several that got away high to the back stop.
For him the "O" is on the side and his thumb is more to the side the ball. Pretty similar to Santana's grip except he grips it like a 2-seamer. He doesn't really put any pressure on the ball with any fingers. He just throws it as he would a normal fastball.
It's amazing how successful you can be with just a fastball and a changeup. And the harder you throw the better your changeup becomes. It's such a weird pitch too. The ball is coming but it doesn't come as fast as your brain tells you it's coming.
Good luck!
Jason