A few times when I've been getting assisted launches recently I've found the top tip of my kite is wanting to fall over backwards rather than support itself.

Is this a result of under inflation/insufficient line tension/launcher holding the kite wrong/something else? I'm only new, but this never happened in a lesson so I'm not sure what I'm doing wrong.

Thanks for your help!

Yep you are too far downwind of the person launching the kite. It is always better to launch the kite slightly downwind. If the kite is launched too far upwind it can easily roll on itself and skid across the beach .Also the person launching the kite should be holding the kite half way between wingtip and centre of leading edge. Only when your lines are under tension and you give the thumbs up should the person launching you let go of the kite.

I actually saw a few launching mistakes today. People throwing kites into the power zone. Giving thumbs up when the canopy is still flapping.. specially at a narrow beach like Melville things like these can end up quite badly.

best advise I can give (even though I am a beginner too)

only give the thumbs up when you can see that the canopy is totally stretched under the wind, no flapping at all. When it is flapping it usually means you just need to walk upwind a bit more as teabaggin said. You should be able to feel when you can launch because of the tension.

try it a few times mate and it becomes second nature!