Please see this page:

http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=167&grha=rhombohedral

The occupation number depends on the actual position of the N-atom. The occupation number of a position is its multiplicity divided by the multiplicity of a general position.

Saying the N atom is on a cell axis is not enough. Imagine that the coordinates are (0,0,0) : the multiplicity of that special position is 2, so you divide 2 by 12 and obtain 0.16667 for the N. If the N atom is on (1/2, 0, 0), or any combination of 0 and 1/2, the multiplicity is 6, so the occupation number would be 0.5. Any other position involving the axis would have an occupation number of 1.