Set exact spawnpoint / underground on MCPC+

hello there, have trouble setting my server spawnpoint underground and on exact cordinates, i tried a few plugins like commandbook, MCspawn and its always the same isse when you spawn the first time you never spawn on the spot you set, you always spawn a few blocks around this area... also when you set the spawn underground you spawn somwehre on the surface. does anyone know a plugin where a can set my spawn that actully works?

note: With my normal bukkit server i never had these problems.