The practical deployment of terahertz (THz) wireless communications requires a proper channel model and an evaluation methodology. For developing THz wireless local area network (WLAN)-type applications, this paper proposes an THz performance evaluation methodology. Also, this paper examines an optimal position of access point (AP) for multi-gigabit wireless transmission, where there exist multiple clusters in THz channel propagation. By considering the multiple clusters for WLAN-type applications in indoor environments, this paper investigates the optimal AP position when two APs are issued for increasing the system capacity. Numerical results reveal that the central position, which offers the shortest cumulated distance for line-of-sight paths, is optimal to achieve the maximal system capacity in THz WLAN-type applications.