The rye baker question on rye flour differences

my first go at this fascinating book. I'm making the berlin cobbler boys - basically dinner rolls using 100% rye, in a mixture of medium rye flour and white rye flour. Unfortunately all I have is dark rye. With the sleuthing I've done and the ingredients I have at home, I chose to substitue 15% giusto ap flour in the sponge (as a sub for medium rye) and 30% ap flour as a sub for the white rye component in the final dough. Does this make sense? 

Its kind of frustrating that Ginsberg hasn't specified some guidelines on substuting for these very difficult to find flours. I know I can get them online but I too don't want to invest in high shipping costs just yet. 

So the rolls look good as I'm getting ready to put them in the oven. Anyone else have conversion guidelines for rye flour? Also I didn't have vital wheat gluten either!

thanks.