Here the results:

0% offset change (stock) => Fuel Trims = +1.73% (FTC 6-14) and +1.70% (FTC 1-19)
+10% offset change => Fuel Trims = +0.14% (FTC 6-14) and -0.91% (FTC 1-19)
-10% offset change => Fuel Trims = +3.12% (FTC 6-14) and 3.39% (FTC 1-19)

The fuel trims values are a sum of LTFT and STFT (this to give a more precide result).
I averaged the counts and not the cells, so those numbers are a weighted average and give the real pictuer of the thing.

The change in the fuel trims is pretty logical.

With +10% offset the car feels stronger while accelerating ant the engine reacts quickly.

With -10% offset something is strange... it's not too bad but it's like an old car with a compression problem. A little asleep

Any comment? What else to try? The result with +10% is really interesting!

I'm sorry but I can't post the graphs. JR: is there a way to upload pictures directly from my PC?