Sorry to spoil your Parade, but.... I think your original tests may only be valid at one condition. Maybe with the C of G in a more rearward position you could have got a better pitch attitude change.
Also when you pulled up (to flair), did you pull abruptly to the back-stop i.e momentarily flew beyond the Stall ?
Mathematically Vx and Vy are linked, as the minimum sink speed occurs at minimum Drag, and this Drag is made up of the Sum of a Square function and an Inverse-Square function. Without going into the Differential Calculus, Vx is always about 80% of Vy.