"There is no such thing as decalage on a monoplane.
It is, by definition, the incidence difference between (or among) two (or more) lifting surfaces.
Many misuse it, referring to the incidence difference between the lifting surface and the horizontal stabilizer, but that's incorrect. "

Actually it can be shown that for a monoplane as well as a biplane that the tail is indeed a lifting surface. For zero pitch acceleration - wing lift times moment arm about CG is equal to tail lift times moment arm about CG. This is true whether conventional configuration or canard.

That being the case the term incidence is correctly used when comparing the angular difference between the wing and horizontal tail.