Need help with Understanding Masonry Fireplace Clearances

[robleonis]

n am installing a Hearthstone tribute in a masonry fireplace I rebuilt. The clearances for a masonry fireplace (with the stove face protruding no more that 2" from the opening) are 18" for the mantle.

What I am confused about is that there appears to be a 9" clearance required between the stove and the top of the fireplace. Is this for combustables or the masonry itself? What is that 9" for in the manual?

Attached is a picture of my setup(mantle not attached yet) and the owner's manual.
View attachment hsmanualtribute8040 (3).pdf

 

[robleonis]

This is the diagram...

 

[begreen]

I added the diagram. My interpretation is that they want 9" clearance to the lintel and 10" side clearance. Not sure why in an entirely non-combustible space but a guess would be that they don't want to risk overheating the soapstone. A call to Hearthstone support may help verify.