Thx okh, never been on source forge, but i may look. Another work around? and working out the centre of a sloping wall, i'll skip that thx [:(]
here is an image, only a screenshot, of the fans location, doesn't seem too unusual :

in it you can also see a similar affect in the 2d window where windows that are in the taller wall also appear to be in the sloped wall.
Mike