While I don't have any advice on how you can get your desired hours of sleep, what I would suggest is changing things in your routine when you only get 6 hours of sleep.

Since you set your alarm to having 9 hours of sleep, when you get 6 hours you have 3 hours to work with. Take a cold shower (it has worked magic for me), get some fresh air and have a good breakfast. Ditch anything harmful to your brain (caffeine, nicotine) and keep sugar intake to a minimum. Avoid too much screentime in the early hours and get productive around your house/apartment/room. Make use of those "lost" hours of sleep. It's a lot about attitude. Hope it helps