I get about 500 maximum, and that's from granny footing.. It's also off 98 RON petrol.. I get about 400-450 generally of a tank of LPG..
What you're getting is awesome.. But if you want to improve it more..
1. Don't carry anything in your car.. Remove the seats, spare tyre, jack, head unit, air bags and all that other useless stuff..
2. Keep your tyres inflated properly..
3. Try not to get above 3000RPM's.. Don't be afraid to granny foot..
4. Use cruise whenever sensible..
5. Coast upto traffic lights, try not to stop, just ease upto them and ease away from them
6. Fit a better CAI, get the engine breathing better.. DIY or buy a kit..
7. If you're still not happy with you're fuel consumption.. Buy another car..
There's heaps more of these tips.. Forget em.. You're probably doing most of them to get 700km from a tank..