Vy equals 1.32*Vx
Lets first agree on the following terminology:
Vy = speed for max rate of climb = speed for max range
Vx = speed for max angle of climb = max lift over drag = min drag
Furthermore it's possible for a jet engine, after a few assumptions and approximations, to mathematically conclude from the drag formulas that Vy=1.32*Vx.
All this seems to be generally accepted and I also find it relatively true when looking at speeds for the B737 and the A320 at lower altitudes. I have not been able to find the relevant data for high altitude.
The question is what happens at high altitude and why? The Oxford ATPL text claims Vy will decrease and eventually equal Vx. Is that true or is the factor 1.32 relevant for all altitudes?