In recent years, the functionality of wireless communications has not only been limited to communication between users, but has also been extended to sensing applications. In fact, several WLAN-based sensing technologies, which rely on changes in multipath radio propagation derived from a channel state information (CSI) in indoor environments, have already been developed. In this paper, we present a WLAN-based outdoor human detection system - the first in IEEE 802.11ac WLAN CSI-based outdoor sensing attempts. The number of multipaths in an outdoor environment is limited, thus, making sensing difficult. To realize outdoor CSI sensing, we present an IEEE 802.11ac WLAN-based sensing system. Specifically, this paper tries to answer the question, How do we install a transmitter-receiver pair? based on an analysis of the experimental results. Moreover, we provide open discussions regarding the optimum installation of WLAN sensing devices.