I find if you are too underpowered it will shoot forward and back while waiting for you on its wing tip. You'll find the right depower.
Exactly - and if really low wind (and/or big kites), it typically wont work always if depowered, as it will drop forward on the nose (LE) too easy, so power it up here.
Or if the beach/ground is not level but pointing a lot down towards the water - then it will also fall nose down if not powered a bit or a lot.
Using a stopper might be necessary then - but always a tricky'er launch when not level.
Otherwise when windy'er, I always let it on half depower or full depower, but that is also because the bar is set this way coming in from the last session (I think everyone or most of us depower the kite fully when walking ashore and on land), so no time lost and no sand to ruin your cleat or anything (as you rinse your trim/bar in the water when you go out - thus REALLY bad to adjust the trim before that as it might ruin it fast...).
For most SLE kites it does not matter how much it is powered, but for some of the less stable ones on the ground, it will influence - but can be both ways it works best - and also dependant on wind.
The reason for trimming full depower when normal wind, is :
If a (upper) rear line catches "anything" on the ground/beach (a little bush or round some grass/straws etc) if you have your lines through "things", and a bit sloppy maybe - it will still not fly up because the rear lines are so slack.
Otherwise, just put it on "half" trim depower if in doubt, which is a good compromise between everything, and you can still steer the kite up - some kites can be difficult to steer if full depower trim
Of course it also depends on your specific setup - some has their initial trim so the kite is not more than full powered when pulled - others set it up so it can be easily backstalled...
And the bar depower "length" (how much it can move forward from the CL) is extremely different on different kitesTypically, the kite IS depowered no matter how you put your trim, as the bar is "full out" always, with a tethered launch - so it actually most often does not matter how you set your depower trim, thus set it halfway or how you left it when out the last time
Sorry - I just discovered now, you were not talking about tethered starting/launching at all, but only "self landing".
Then just full depower trim always - even if it goes LE down, you have landed (and you can give it a tuck on the upper line to sit perfect so you dont have to walk out to the kite)