AFAIK it fights to its front and has enemy in contact with its flank - so it is destroyed if it loses. it is not in a tower so there is no reason to assume that it would fight in that manner as far as I can see.
However I can't actually find the bit that says that contact with a TF is the same as contact with an element behind it - I used to know where it was in DBM....but can't find it in 'MM
P35, top, initiating a close combat with an element includes contact "with an intervening fortification".
P37 Tactical factor -1 for enemy elements in front edge
combat (
not contact) with a side or rear edge.
P38 Outcomes for less than but over half: destroyed if enemy "in
contact with its flank" (
not combat).
So the defender gets a -1 tactical factor but does not get quick-killed unless it would have been anyway.
(unless someone
can find a bit that says that contact with a TF is the same as contact with an element behind it )