In one embodiment, an access point of an overhead mesh of access points in an area selects a range of client identifiers. The access point sends, via a beam cone transmitted in a substantially downward direction towards a floor of the area, a trigger signal that includes the range of client identifiers and prompts client devices having identifiers in that range to send best effort transmissions towards the overhead mesh. The access point detects a collision between the best effort transmissions of the client devices. The access point adjusts the range of client identifiers so as to avoid future collisions between the best effort transmissions of the client devices.