On Vehicle-to-Everything networking, Vulnerable Road User (VRU) is the name attributed to traffic members that are at a higher safety risk in mobility systems, such as pedestrians, cyclists and road workers. VRUs transmit VRU Awareness Messages (VAMs) to actively broadcast their position and kinematics to other traffic members and road infrastructure. Through the exchange of VAMs, the VRU Basic Service contains a clustering functionality that groups VRUs with similar behavior to prevent channel congestion in crowded traffic scenarios. A cluster leader is responsible for transmitting VAMs that describe the group, generating a bounding box geometric shape that describes the space occupied by its members. The current VAM standard however, does not provide strategies to produce these shapes and does not elaborate on methods to evaluate shapes. This work offers algorithms to construct these geometries and discusses metrics to compare the generated bounding box types. Simulation results show that each shape type can be useful in distinct use cases. It also shows that changes must be done in the currently proposed standard operation message triggering, as the results indicate that channel occupation was not mitigated by the functionality.