You may note that I've started carrying my sit on top like a canoe. Hull to the sky, directly on the bars with no racks. I've had good luck doing this with poly boats, but this is the first time I've done it with a composite boat. so far it is working well.
Here are the contact points on the bars:
On the back bar you can see the corner of the Scotty mount base. I installed one behind each hip in the back. One for a camera and one for a rod or light. They also serve very well to keep the boat from sliding forward. I've been using a bow line to the front of the car for a safety factor to prevent the boat slipping backwards. Now that I don't use foam pads or saddles the boat is far more secure and you cannot wiggle it without moving the car after the first strap is tight.