The receiver efficiency in radio-frequency (RF) energy harvesting (EH) is affected by numerous parameters such as the average RF input power and peak-to-average power ratio (PAPR) of the waveform, the EH circuit components, and the load. In this paper, we experimentally study the dependence of RF-to-DC efficiency on these parameters. We present a test-bed, comprising a signal generator and an off-the-shelf energy harvesting receiver with a diode-based rectifier, for evaluating the RF-to-DC efficiency for varying input RF power, load resistance and a number of co-phased baseband multisine waveforms (viz. PAPR). The experimental results suggest that the RF-to-DC efficiency of multisine waveforms in RF EH is significantly affected by the average input RF power and the load resistance. The high-PAPR multisine waveforms are preferable for RF EH only for a certain range of average input RF power and load resistance. In particular, for the considered rectifier, a single-sinusoid waveform yields the highest RF-to-DC efficiency for low-resistance and high average input RF power region, while high-PAPR baseband multisines are optimal for high-resistance and low average input RF power region.