I have read some about "frontal bone prominence" reduction. From what I have seen mentioned, it depends on the thickness of the bone and that needs a high def CT or similar scan so the doctor knows what they can or cannot do.
What I see written most about is the frontal sinus cavity and supraorbital arches, as well as the rim for some patients, being the primary reduction target. If the frontal sinus extends forward, then some surgeons will thin and pressure the bone while others cut it out and reset it. That is called a type 3 forehead reduction. From what I've read a type1 reduction is when the sinus cavity does not require any work on it directly.