Math for blending a medium rye flour
I'd like to try out "Hans Joakim's" rye recipe that is on this site  which calls for a medium rye flour, which I do not have.
My problem is that I have a plain bag of some flour simply called "sifted rye flour", it comes from a farmer who only delivers in brown bags without any writing so no idea of the extraction rate he managed to achieve in the sifting. I'd like to blend this with some wholemeal rye flour to make the medium rye flour.
Guess I have to make some sort of rough estimation to do this blending. I see that Stan Ginsberg was in a discussion on this site in 2018  where he said that medium rye is about 85% XR. Now, thumb suck, assuming my "sifted" rye is say 60% XR , I'm guessing that if I were to blend say 62.5g of rye wholemeal with 37.5g of the sifted rye I should come up with something like a medium rye flour? To keep things simple I'll probably go with 60 WM:40 sifted. Does this sound like a good enough guess?
Thanks and sorry for bending anyone's head with math!