Instead of entering a radius value, you can use a "hold curve" to
compute the fillet. Depending on the curve's shape, the fillet's
radius value is then more or less variable.
Select both faces as shown then expand the dialog box to access
further options.
Select Join.2 as the hold curve.
The curve must be sketched on one of the selected faces.
Select the spine you want to
use.
The spine provides a better control of the fillet.
To compute the fillet, the application uses circles contained in
planes normal to the spine. It is then possible to control the
shape of the fillet.
Preview the fillet.
Repeat the operation and select this spine.
The fillet has a different shape.