Contention-based Geographic Forwarding (CGF) is a state-free communication paradigm for information delivery in multihop ad hoc and sensor networks. A priori selection of the forwarding area impacts its overall network performance and the design of the CGF protocol as well. In this work, we study the fundamental problem of defining the forwarding area a priori for CGF and determine its impact on the performance. We model CGF without void (i.e., absence of a next-hop node in the forwarding area) handling as a 3-step forwarding strategy. Based on this model and given a random distribution of network nodes, we develop a general mathematical analysis technique to evaluate the performance of CGF with different forwarding areas, in terms of the performance metric average single-hop packet progress. Further, we introduce two state-free void handling schemes, i.e., active exploration and passive participation, for CGF and study their performance in depth. Our theoretical analysis and numerically evaluated results, validated by extensive simulations, provide a guideline regarding the selection of specific forwarding areas for the design of a practical CGF protocol. It also serves as a general performance evaluation framework for the existing CGF protocols.