You may want to calculate the wing area again. I used 1" square grid lines for the wing tips to subtract that area from the total wing area and I came up with 1408 sq inches, over 100 sq in more than GP states.

The center of the lower wing lifts too, so you have to count that too in the area. I even subtracted out the semi-circular cutout in the top wing.

This makes the wing loading down in the 26 oz/sq.ft.