User blog comment:IamJakuhoRaikoben/Chapter 412: Dance Unto Ishgar, Review./@comment-24784846-20141208205033/@comment-7418318-20141209004223

Another point:

Maybe it's just perspective, but aren't the Faces other a lot bigger than the first one? Maybe that means that the first one wasn't fully out of the ground yet and that Wendy only destroyed part of it, but not enough to impede the function.

Or it was a different kind of construction due to being the intended trigger mechanism, though obviously there was another way to fire them in case the control unit is taken out.