We discussed this issue with Achille, so the Number of Objects counts only the marker of the door (if it is in the area of the zone), not the door itself.
"The Walls Perimeter" lists the perimeter of the walls bounding the zone no matter how many openings are placed into the walls.
In the wall list the Conditional Length parameter takes into count the length of the doors.
Gabor Almasi
Senior Product Manager
GRAPHISOFT