Chuck,
The rule of thumb I use is a little different from your's. Approach is at 1.3Vs for slopes up to 10%, then - in theory - you add 1km/h (French aeroplanes.....) per % after that. Obviously things aren't as precise as that in real life, but you get the idea. So for a 25% slope, I'd be looking for an approach 15km/h faster than normal. For some short strips with a level touchdown point, a slightly slower approach is sometimes used if conditions are calm.
Power is kept on somtimes until contact is made, especially when using skis in the winter, then reduced momentarily to ensure you're firmly down before adding power again to climb the slope.
The wind and thermals can often conspire to mess things up nicely, though!
This strip (also
here ) is a case in point. It's 320m long, 10m wide with a 17% slope (concave then convex) at 6300ft altitude. In a headwind or crosswind from the right, the approach is flown in a descending airflow, which in summer is punctuated by vigorous thermals coming off rocks that are exposed to the sun. The density altitude is high if it's hot, and an on/off button would sometimes be more use than a throttle lever!
I'm afraid of breaking things (especially myself!) so I don't go there alone except when things are nice and calm!
Kanobea looks entertaining. I imagine with all those ridges the approach is a bit bumpy whatever the wind direction...? From the photo, it looks at least that you have an escape route to the right.
You also have a nice juicy variety of tropical bug that must help you to fix the aiming point! Do they bite?
