Implantable bioelectronics require highly efficient wireless connectivity for autonomous operation and closed-loop control, yet power constraints, safety regulations, and data transmission limitations continue to hinder advancements in medical device innovation. This study systematically investigates radiation loss mechanisms and proposes strategies to improve electromagnetic efficiency in wireless implantable systems. Utilizing spherical harmonic analysis, we quantify radiation efficiency and in-body path loss through rigorous closed-form electromagnetic modeling, identifying three primary loss mechanisms. On this basis, we introduce a rapid and accurate estimation technique to optimize the operating frequency, complemented by design principles aimed at augmenting radiation performance for robust wireless links. The proposed strategies, substantiated through comprehensive numerical and experimental validation with realistic implants, demonstrate a potential 5- to 10-fold improvement in implant radiation efficiency or gain, offering significant benefits for early-stage implantable device development.