Wireless power transfer (WPT) offers practical solutions in modern power systems for electric vehicle (EV) charging, smart grid integration, and consumer electronics by providing efficient and contactless energy delivery. This paper focuses on designing a high-efficiency WPT system based on magnetic resonance coupling (MRC). While conventional studies improve efficiency by adjusting the distance between the driving loop and the transmit coil, this paper highlights a novel method of enhancing efficiency through radius optimization of the driving loop. By tuning the loop radius according to different transfer distances, the system achieves improved coupling coefficient and higher efficiency. Experimental results confirm that the proposed method achieves a relative improvement of approximately 38% over the baseline system efficiency, while maintaining consistent performance across various transmission distances. The proposed radius-tuning approach provides a simple yet effective means of optimizing coil geometry without requiring complex control strategies or system modifications, offering promising applicability for wireless charging of electric vehicles and consumer electronics.