A vehicular Ad-hoc Network (VANET) is a wireless network established between vehicles and surrounding infrastructure to enable information exchange between them. Consequently, many applications that can enhance passengers' security assurance and traffic flow are built upon this information. However, malicious nodes can manipulate the exchanged data to attack other nodes and disrupt the network’s normal behavior. For example, if an attacker broadcasts a falsified vehicle’s location, the functionality of applications that rely on accurate location sharing will be confused, and deadly accidents may occur. Thus, many studies have been conducted to implement Misbehavior Detection Schemes (MDSs) to identify position spoofing attacks in VANET. However, the performance results of these MDSs are limited in detecting some attack types, and most of them rely on application layer features that the attacker can alter before transmission to evade the detection model. So, this paper proposes an MDS for position falsification attack detection that employs a physical-layer-based feature called RSSIConf. The RSSIConf feature relies on the Received Signal Strength Indicator of received messages and its confidence intervals at different confidence levels and distances. The evaluations show that the proposed model outperforms existing approaches, where the improvements range between 0.76% to 13.26% in accuracy and 0.74% to 12.71% in F1-Score, depending on the detected attack type.