Ionization structure perpendicular to the line of sight can cause total internal reflection at glancing incidence, leading to refractive scattering that can dominate diffractive scattering. The long-wave cutoff in the spectrum of amplitude fluctuations then occurs, not at the Fresnel scale but at a larger scale that increases as the percentage fluctuation of ionization density increases. The additional amplitude fluctuation arising from the band of scales extending from the usual diffractive cutoff scale up to the refractive cutoff scale is capable of explaining strong SHF scintillation. It also lowers the estimates of the fluctuation of ionization density needed to explain strong VHF scintillation. The concept of refractive scattering is also likely to be applicable to SHF-EHF scintillation phenomena in the troposphere.