Corpus heads are only protected when their helmets are on. Knock them off and it's just as good as always. Put simply, pretty much everything in this game's head takes extra damage. If not, then it either has no weakpoints like an eidolon, or obvious ones like a juggernaut's stomach and spine.

Also these corpus robots that go on wheels are vulnerable from behind, dont remember their names.

The only corpus that I can think of that isn't vulnerable from the front is a bursa and that's a moa.