Hi Mauro, so some additional specific details:

"Normal" mode actually uses the default relative tolerance (0.001 if your object is between 1 and 50 units in size, otherwise a fraction of the curve's bounding box size) for the outer boundary curves and 10 times that amount for the tolerance of the interior curves.

"Lighter" mode uses boundary tolerance of 15 times default tolerance for outer boundaries and 30 times default tolerance for inner boundaries.

"Custom" mode uses the value you set for both boundary and inner fitting tolerance.

"Uniform" mode uses the given number of sample points rather than doing a tolerance deviation based fitting.


Also if you are doing a 4-sided network with no interior curves, there is also an "Exact" setting available that uses the curves as-is (inheriting all curve structures into the result surface) with no refitting done at all.

- Michael