Consider an axially symmetric, toroidal, magnetized plasma with some safety factor (q) profile. A flux surface has q=m/n where m is the number of toroidal transits and n is the number of poloidal transits for a magnetic field line.
Why do the dominant modes have low m and n? For example, q=99/100 and q=1/1 have almost the same curvature, but q=1/1 is the more important mode when considering instabilities.