If you are going to have the rotors extending over the top of the fin I suggest that even a low fin is likely to suffer `rotor strike` at some stage. A very low fin may be OK, together with an underfin and also tip fins on the stabiliser - but even they need to be mainly below the stabiliser and very little above it. See my modified Gyrace (now a single rotor autogyro on my webpages mentioned the other day). I found I had to cut down both fin and tip stabiliser fins and extend them `down under` to compensate. I have also had rotors hit the fuselage on aircraft that have rotors that don`t extend over the fin.
Autogyros have their challenges, but it is great to achieve success.