If you tend to look closer at the requirements for operating into and put of MILITARY aerodromes, they require you state POB on initial Taxi call! Darwin is a dual military/commercial aerodrome and that is why they controllers are asking you to state your POB... Devosh!
Also I sometime operate a pressurised aircraft, VFR at flight levels below FL180. when you think no one is listening to craft, think again... it is a requirements for our company to listen to both CTR and CTAF FREQUENCIES when able. So when I'm on decent from FL150 to my CTAF at 25NM, chances can be that I'll conflict with outbound Metro traffic departing for a hop skip jump at FL120, on my decent.
So Yes... it can and does happen. Just because you cruise above 10000ft doesn't mean your oblivious to what's happening underneath you.
Simple answer just say the FL on climb to. How hard is it! Maybe I'll start saying "climbing altitudes" when I depart a CTAF and see how the traffic inbound takes it. I'm sure the radioactivity will get clogged then!
