Contact resistance (R_C), which dominates the performance of organic field-effect transistors (OFETs), relates multiple factors such as charge injection, transport, and device architecture. Here, we focus on physical meaning of the convergence point in conventional transfer-length method, and clarify the correlation between charge injection and geometrical parameters of OFETs by simulations. We also defined the effect of band-like/hopping transport in semiconductor on the charge injection process, where less hopping transport results in lower and less gate-voltage dependent R_C. These results were confirmed by experiments on pentacene OFETs and reveal the values of convergence point in OFET research.