The game does not recognice the three locations south of the activator rail as a valid spot to eject a player/mob.
Forcing the activator rail to eject towords south (south, south-east or south-west) by blocking all other locations will eject you or any mob on the activator rail as if there was no valid spot. (setup as shown in the pictures)
There is no difference in the rail going north-south or east-west.