This new length of the flat is not a new diameter for a circular flat. In the vertical plane, the old diameter of 1.30" remains the same.  Thus the old circular flat has been stretched into a new elliptical form, with a Major Axis of 1.85" and a Minor Axis of 1.30".
Now that the flat is larger, it is time to recalculate the telescope's new Clear Aperture.  As can be seen, I have dropped a line from each point where the flat intersects the Light Cone down to the Mirror's Axis of Symmetry, giving me two new triangles to solve.