The study of gamma-ray burst (GRB) afterglows across the electromagnetic spectrum can reveal a lot of information about their jets and surrounding environment. The physical parameters of the GRB jet and emission processes at its shock front can be constrained by broad-band modeling, but individual parameters can in some cases be determined by a limited number of observables, which can be used to independently constrain the models themselves. We expand upon a method using peaks observed in afterglow radio light curves to constrain the fraction of the shock energy that resides in electrons, εe,weakly depending on other physical parameters. We use both light curves and radio spectra to determine the peaks, allowing for a systematic check of the modeling approach. We also expand the sample of 36 radio afterglows in the initial study with 15 additional GRBs that have good radio data available. With this expanded methodology and larger sample, we assess the initial results on the width of the distribution of εe,which provides important input on GRB shock physics.