In my testing, I believe the zone uses the base of the wall to determine its extents and therefore its area.
If the wall base is below the floor (storey) and the window is above the wall base, then the zone will not include the reveal in its area.
No playing around with the sub-floor thickness in the zone or the window seemed to make any difference.
I find that the window must be at the wall base for the reveal to be included in the zone area.
I would say this is a bug as the area of the zone (I think) should be taken at the base of the zone - not the wall.
But I may be wrong as I don't use zones with room areas very often.
The only work around for now that I can think of is to manually adjust the zone - but you will lose all automation.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11