This decal feature appears to be somewhat buggy, unpredictable and sometimes crash seeking.

I have a U shape part with angles verse curves.

Apply the decal to the extruded surface,  the Decal feature allows you to use "Label" as an option and the application works as expected.  The bottom point is the center for the decal and wraps across to the sides.  Lovely.

However, make the part as the final solid and