The spawn-protection option in server.properties appears to also be the area size that players will spawn in.

Documentation implies that players will spawn in a 20x20 area around the worldspawn point. When the spawn-protection is set to a high value (400) players are able to spawn that many blocks away from the set spawn point. Setting the value low (5) will spawn players as expected.

My world has a custom spawn point inside a labyrinth. I'd like to be able to use the spawn-protection value to prevent breaking through the labyrinth but need to be able to control where players spawn.