My units are on a Gully and I have played a (single) forward movement on them.
The enemy attacks me at range 5 (so he can).
Correct. Or he could do it from a Hill.
What is my terrain defensive bosus, -2 or -1 (= -2 + 1)?
The first movement card is ineffective even if I am attacked from range 5?
Total Defensive TEM would be -1: -2 for Gully +1 for Movement.
The "hidden" movement card only applies when a group has 2 movement cards to leave a Gully (which normally would be considered entirely out of terrain.
Lucky I checked the 'geek just before the WBC Up Front tourney which starts in a an hour.