Hi Tommaso,
Look at the scaling factor displayed in the results window itself. In the first case (10%), it's 4.7315. In the second, it's 10.00, exactly as you told it to do.
Gunter is correct: 10% means "make the maximum deformation 10% of the 'model size'." In this case it scales it to be (9 × 4.73 = ) about 42.6, so the 'model size' (bounding box diagonal) must be about 426.
We've already had a similar discussion!