scope rings

[cbr1100]

I finally got my arms 18 mount installed today and proceeded to install my 3200 5-15 scope using medium rings and ran into some trouble. The scope won't fit as in hits the rear sight, it is not even close. How much taller are tall rings compared to medium?

 

[cbr1100]

I tried some cheap med rings I got at the local store and they fit. I don't know how they will stand up though. I will look at getting some better ones soon. What would you guys recommend for ring to use with the arms 18 and 5-15 40.