last 6 months - posting preference

I was led to believe that in your last 6 months you could request a posting to the area in which you intend to settle.

My questions are
1. Is this true?
2. Where is there an official reference to this so i can quote it in a letter i need to write?

Any help would be appreciated as my Clerks are useless !!!

After your MINIMUM time is up you may request a posting NEAR to where you would like to settle!

This isn't a guarantee that you'll get it though!