The slope rating came from the guy who invented the Slope rating ( Dean Knuth ) - so I don't know what to tell you
This is what he took into account:
RATING AUGUSTA NATIONAL
Following the USGA formula for rating courses, I graded each hole at Augusta National for 10 obstacle factors on a scale of 0 to 10. The rating criteria:
Difficulty of stance in the landing area and the vertical angle of shots to the green from the landing area. The par-4 11th, with a downhill stance and long downhill second shot, gets the highest rating, a 7.
The effective target size of the landing area with the hole length factored. The 465-yard 18th, with a full dogleg right that squeezes the landing area between large fairway bunkers to the left and trees to the right, also gets a 7 rating.
Recoverability and rough.
The par-3 12th rates highest with a 6. No U.S. Open rough at Augusta National keeps this rating category from being in the Open range of 7s to 9s.
Out-of-bounds or extreme rough near the landing area and green. Nothing higher than a 2.
Difficulty of this hazard as it comes into play. The par-5 13th is an 8 with water running along the left, forcing drives toward the right trees. For those going for the green in two, there is a very difficult crossing stream that catches shots coming up short, and the green slopes toward the water and is squeezed by bunkers in the back.
Strategic location of trees, size and height, and their effect on drives and approach shots. The 18th leads with a 7.
Location, size, depth of bunkers relative to landing area and green target difficulty. The 18th again rates highest with a 7. The fairway bunkers on the left are forced into play by the dogleg and right-side trees. The approach from the deep fairway bunkers is a very difficult uphill shot, and the greenside bunkers are deep and strategically placed.
Getting onto greens in regulation, affected by the size, firmness and shape of a green in relation to the length of the approach shot. A tie with 8s for the 10th, 11th, 12th, 13th and 18th holes. The greens have multiple small target areas depending on the hole placement, with difficult approach shots.
The slope, contour and speed of the green. This is one of the most notable features of the course during the Masters. Holes 1, 10, 11, 14, 15, 16, 17 and 18 all qualify as 9s with difficult hole placements, high contours and swift Stimpmeter speeds.
The mental effect on score created by very difficult obstacles near the target areas. Holes 1 and 18 are both 8s. The starting hole and the finishing hole always qualify for some values, but both of these par 4s have a collection of highly rated obstacles, giving an overall mental impact.