trying to interpret what you said, u were placed into a expat after your probation ? or shld we interpret it that you are given a raise in the form of a housing allowance after your probation ?
expat contract actually means the person continues to be employed by the head company that sends the person over. the orginal basic pay remains, and any cost including housing, schooling, living expenses, etc, are paid in addition to the person. when the person goes back to the hq, the benefits are taken away.
rental apartition of pay is applicable even to local hkers. not just foreigners.
and on the other point about putting 10k as housing and 15k as base pay. to do that, one would have to provide the necessary paper trail in case IRA decides to check on you. i doubt anybody being paid 25k p/m would want to rent a place that cost 10k. so eventually you only allocate your actual rent of your pay for the tax considerations.