Hi There,
It reduces a little bit of oil every 3-4K Kms. Sometimes it doesn't reduce any oil for 6-7K kms. It basically depends on my driving pattern. I had been driving it in a more "civilized" manner for the past few months since my parents were over
.
However, now that they're back in Pakistan and we've entered boost friendly weather, my current boost gauge history shows a peak boost of 18 PSI 
I change oil every 10K so in order to be on the safe side and keep the oil levels up to the mark, I get it checked and topped (if required) more frequently than I probably should.
As per Subaru, this is expected behaviour. Most of my friends who own certain Audi and BMW models experience similar engine oil consumption. For example, my friend's BMW 535i in the picture below needed 1 quart of engine oil roughly every 6-9K Kms.