"Depower" your kite then send it through the power zone and tell me if you've reduced the power in the kite at all... It's a trim system, not a power-limiting system.
IMO the important thing about trimming a kite is to set it all up so that you can maintain a good body position ie. a good stance... You and the kite should then be in the best set up for most efficient aero- and hydrodynamics
Many (most?) kites are designed so that if the lines are equal with the bar pulled in, then that's the perfect trim; don't over-think it. Unless you're racing...
If the kite is too powerful, then it's a sign you need a smaller kite and vice versa.
Ok here I go again! Power comes from wind generating lift as it goes over the kite. Same as an airplane generates lift. Kite shape, size, air density, and apparent wind are the main factors in power.
There are 3 points of trimming the kite.
1: at the kite where you attach your lines.
2: your trim strap (depower strap/rope).
3: your bar throw.
I personally trim in this fashion. I use the attachments at the kite to adjust for line stretch so I don't have to all ways tune my bar. I do most of my trimming at the trim strap. I know from experience where I should be. Things I look at is shape of kite in air, are my wingtips flared in or out, is the kite flying over my head or backstalling. When I unhook how does the kite react, how is my bar pressure. I look at all these things to determine if I need to trim.
As far as power goes. I fly 7/9/13m Fuels I do from time to time ride over trimmed on my 13 at it's top end before I might switch out to my 9. But in general if I have pulled 4" or more trim I know I need to switch out to a smaller kite.
Biggest thing to learn is that Power is kite, and Trim is how well it flies. Kites are not cars they don't have a throttle. It's a trim strap not depower strap!!!!!!!!!