Oh dear, oh dear.
Since 2009 housing prices have risen by 80%
OK
So, your $10,000 HKD housing allowance over a 4 year period is worth in real terms $2000 HKD.
No, in real terms that $10,000 is now worth about $5,555.
If housing prices had doubled (which, China Beached, is more than 80%, in fact its an increase of 100%), then the real (ie inflation adjusted) value of $10,000 would have been halved, ie $5,000. Still more than twice your claimed value of $2,000.
Let's put it another way, if housing prices in 2009 were $4,000 per square foot and then they increased by 80% they would now be $7,200psf. In 2009 $10,000 would have bought you 2.50sf, now it buys you 1.39sf. (note that 1.39 is sitll about 55% of 2.5, not 20%)
Now you claim that $10,000 today, in real terms, is equal to $2,000 back in 2009. If that were true then $10,000 would only buy 0.50sf, which is what $2,000 bought back in 2009.
Please tell me you were joking.