I havent seen this thread before it was linked to from the hydrofoil section now
or6 you are wrong, if you and your kite drift in the water in zero wind, but current, you will still have the same wind at the kite and be able to relanch, as if it was no current and the wind blowing at the same speed.
The wind gradient matters yes, but they would be somewhat the same "size" so no problem there either.
Sorry to say, but you somewhat got it wrong - you are talking about zero wind and running, but when you got current in no wind, it is exactly the same as having wind blowing and no current, that is 100 % for sure
If you are riding in current and can not jump like you are used to, it is because you have chosen the wrong kite size - as if current is upwind you should choose a smaller size, and reverse, downwind current means you need a bigger kite.
Simply because it is only the wind versus the current speed difference that matters, nothing but that, regarding kite size and power.
Choosing your kite on this, will make your jumps exactly the same no matter which direction the current is.
Of course you will have more or less ease keeping ground relative to the shore, but that is not the topic here...
Think about it once more, or twice, it is very simple when one think in relative terms
I know many can not grasp this, as it was the same issue most had with the "max jump" height, but no doubt it is how it works and not just theory.
Alex and edt and others are spot on or6.