Alex, hard to say what would be the cause of the difference that you noted. Could be the shape of the hull (Panope is full keel) or proximity/shape of the rudder.Glad to hear that you are feeling better!
This test has forward and reverse bollard pull tests of a lot of props, including a standard 3 blade prop that should be similar to yours:
They only show about a 40% decrease in reverse compared to forward (265kg vs 163kg), where you are seeing a 67% decrease. I wonder what accounts for such variability? Their boat is obviously very different (it is a fin+spade modern cruiser).
They are using a smaller Yanmar engine, but with the same gearbox as yours.
Also, I noticed that my gearbox has the choice of three different forward gear ratios and only the one reverse ratio.