Well, I found those clear hexes immediately surrounding the building to be mostly non-zero height. Tried leveling them individually using the asterisk key but then the entire building hex reported zero height. This confirmed my earlier conclusion that an "elevated" building in WinSP map requires the so-called "height-supporting hex" that must be a non-building hex; without this "support pole", the entire building hexes would yield zero height. Maybe you misread the height report (on the top red bar) of those surrounding hexes. Sometimes you need to move/scroll the map a bit for it to report the height correctly, like after altering the height using the asterisk.
This is what the map looks like (with my two "elevated" buildings on the right). It seems that using multiple "supporting poles" would reduce excess height reduction on the building hexes. Using just one support pole (the building on the center), the maximum height for the building hexes is 87. When using three support poles, each 200 (building on the right), the maximum height for building hexes is 170.