Fig. 1 below indicates that the supermumeraries of the primary rainbow (for water droplets of radius r = 100 µm) require fairly uniform drops.  There is little difference between standard deviations of 1% and 5%, but the supernumeraries disappear for 10% and 20%.

Scattering angle (degrees)	Scattering angle (degrees)

Fig. 1   Primary rainbow: effects of disperse drop size (nominal radius r = 100 µm, λ = 0.65 µm)