When sheeting out the Cloud one wants to loose power, but the kite flies back towards the power zone. Isn't this a contradiction ?
It is sheeted out, it gives less power, no contradiction.
If it is not sheeted in enough to make max lift, it doesn't matter that it is in power zone (until way overpowered).
Sheet in and it edge and the cloud makes power and moves forward in window, and you can head more upwind. Ride along on a reach with the Cloud luffing somewhat, even though it's sitting deeper in the power zone, it is not pulling hard.
Now back to the learning thing, about this power zone....
Why is there a power zone, why do we perceive this effect of a power zone?
Imagine riding on a reach with the kite at 45 degrees.
Is it in the power zone?
If it is "in front" of you, with lines running almost 90deg to your track, it is not in the power zone, it is at the window edge.
If it is "behind" you, it is in the power zone, and will pull harder, and you may feel it is pulling you downwind.
What is the angle of attack?
At the window edge the AOA is low. Want to move the kite back in the window? Sheet in.
In the power zone, the AOA is high. Want to move kite forward? Sheet out.
The "power zone" concept basically describes how the AOA over the kite changes as the kite moves around in relation to the rider.
Moving the kite around the window is the "advanced" way of adjusting the kite's AOA, why with old C kites ( and to a degree new ones) you stomp the edge to force the kite forward to window edge to depower it, ride at it then turn away to to put it into more power.
The changes can be extreme, to choke power out of an overpowered kite, or load and pop to jump, or subtle, as in creating a wake that's not a straight line but more of a sine wave as you deal with chop or gusts and lulls. The way you edge or point the board can be the fine trim on the kite as well, moving the bar can be a pretty coarse adjustment with some bridles. With a true old school C from 10yrs ago, it's sort of the other way around, the bar throw and depower are quite small, and really using the board is required to get the most from the kite.
Further confusing things, struts that stabilize the canopy are like full battens in a windsurf sail, they keep some camber in the canopy so even at zero AOA it makes forward lift, in some cases leading to hindenburging out the front of the window.
So people are used to making coarse bar adjustments, and relying on the locked in camber of the canopy to keep the kite driving.
With no struts, sheet out and the canopy instantly loses part of its profile, flapping and reducing the lift, and letting the kite drift back in the window. But since it does not have the full camber, it does not pull hard or make much lift, it will sit back there where you put it.
Ill give it another try when I get a chance and will keep exact measurements of my bar movements
Good plan, I'm sure you have a micrometer sitting around somewhere...