If you set -fat or -narrow values to "256,256,256", there will be huge collision boxes. So, if you set ".fat/narrow=on;", you'll need huge rooms to move in.
Look at your model's first frame in MED. Where is the centre?
Look at your model in WED, it's properties, its bounding box.
Look at your model in WED, zoom it in, move your mouse vertically/horizontally from edge to edge. What's the mathematical difference shown in the menu bar? That's the size you should base on with hull (level-building) or min/max (scripting) values.
Not sure if that helps.