The /gamerule spawnRadius <amount> command is effectively ignored, although the server is entirely able to set and get its value. Upon death, the player is always spawned at the exact location of the world's spawn, no matter what value spawnRadius is set at. The behavior exhibited in the vanilla Minecraft server is to always spawn a player randomly within the given spawn "radius" (a square area) from the given world spawn coordinates. While there is a workaround possible with command blocks, it, for obvious reasons, reduces overall server performance.