The lowest point and the point you contact (trust me!) is the small wind splitters that are molded in. They are lower than the rectangle for the license plate in the front.
The distance from the center of the tires on the ground to the first point on the splitter wings... is 28.5".
On the LSS car, they are 5.75" from the ground. That is 11.4 degrees.
On a non-LSS car, obviously it would be a little better.
I really don't think it matters about the angle of attack. The splitter wings will be about the same distance and require the same angle of clearance even if you came in at 30 degrees or even 45 degrees.
I do think it matters that you go very slow, since the compression of the car's suspension will temporarily decrease the clearance and you want that to minimize that.
And also.. don't do what I did. Watch out for the small bit where the driveways merges back up into the curb. Where I hit was only 1.5" high... but it was enough to cause damage.