The nsewu models for fire have a misplaced face. When looking at fire from the top, it should appear to be a funnel - as in, it has four faces that are rotated so that they face upwards, closing to a point near the middle.

There is one face (facing North) that is rotated in the wrong direction, which makes it face downwards where it's almost invisible.

Here's a pic of the fire from the top; http://i.imgur.com/nUwWLxB.png
note how only three sides are facing outwards.

Here's a pic from below: http://i.imgur.com/aC3KVhD.png
The face outlined in red is facing north, but is rotated in the wrong direction, pointing downwards like / instead of upwards like \