Both triangles are 45° triangles where the hypotenuse is known. I have labled the vertical side of the upper triangle, "h," and the vertical side of the lower triangle "s."  h = c sin 45° = 0.7166" and s = c' sin 45° = 0.5947".
Adding h + s gives a total obstruction of 1.3113" which is only 0.0113" larger than the obstruction offered by the circular flat. Essentially there is no change in the magnitude of the Clear Aperture. There will however, be a change in the shape of the Clear Aperture.