Efficient heteronuclear decoupling is essential to obtain high-resolution NMR spectra of organic and biological solids containing protons and low-gamma nuclei such as carbon-13. All modern decoupling sequences employ pulse lengths that are optimized for a given radio-frequency (rf) power. However, there is an unavoidable distribution of rf field amplitudes across the volume of the sample. Inevitably, the effect of the rf field distribution manifests itself for fully packed rotors during any decoupling irradiation. In this study we present a detailed analysis of the effect of the inherent rf field inhomogeneity on decoupling by the low-power phase-inverted supercycled sequence for attenuation of rotary resonance (PISSARRO). This reveals a potential for further improvements of its efficiency.