Well, I didn't think I would have to include the exact swing angle..but,
...If the ball is met 1/2 inch below the center by a bat moving in a slightly upward (10 degrees or so) direction at a speed of 80 mph or so...the ball should go about 370.
My point was that there are more important factors to driving a ball 370 ft...path of swing, speed of bat, point of contact on the bat...getting backspin from a downward swing angle is not a actual factor...