In this paper we present our investigation on the impact that different packet types (data, management, control) have on the signal strength values observed by access points. Signal strength is often used as the major indicator for client location in WLAN location determination systems. It is vital for accurate prediction that the signal strength distribution and its variations is understood and modeled as closely as possible. We show that different packet types result in significantly different signal strength distributions and that a location determination system should therefore distinguish between the packet types and use the appropriate distribution for each packet type.