Set a place’s “Customize Reserved Server Slots” to 3
Observe that on occasion, using TeleportAsync to teleport a single player into that place will put them into a pre-existing server; this appears to have some relation as to whether or not that player has a friend in the pre-existing server
This feature is intended to be used to help users be able to join their friends more easily. The reserved slots will be unavailable to users unless they are friends with one of the players already on the server. In your case, this means that teleporting a single player will put them in a pre-existing server if the player already in that pre-existing server is a friend.
Let me know if this tracks with what you’ve observed - from step 3 it sounds like you’ve observed this.
In that case I’d say this works as intended, but IMO the name and blurb do not convey this nuance. I read it more along the lines of “these slots will be reserved for developer custom matchmaking logic.”