Below 40%NRP and above 75%NRP detonations and preignition are most likely to happen. Still, as stated above, it's extremely rare. But during a long taxi pay close attention to your mixture setting because running to lean with an air-cooled engine at less than 40% will cause a nice rise in CHT.
Yann
Edit: forgot to mention that when running to rich carbon deposits form in the cylinders and can cause detonation, so leaning is good practice during taxi.
