I agree with your thoughts on how to use it - try to secure a flank with a strip of DGo which your elements stand behind. However, the downside with static defences is that they can be walked/driven around (i.e. the Maginole line).
I agree with that sentiment. You might get something which protects you to your front, in which case the enemy will attack the other flank, or flank march around it. Or do what Claudius Nero did at the Metaurus when his troops faced Gauls sitting on top of a large steep hill: ignore them and march around behind his own army to attack the opposite enemy flank. And the Gauls just sat up there scratching their backsides.
The next problem with relying on terrain is that it requires you to always be the defender - if you're unlucky enough to be the invader, you're in trouble, unless you can manufacture something out of the enemy's terrain list. Now I used the same trick a lot in DBM with Hellenistic Greek Aitolians: Aggression 0, lots of terrain, and lots of Ps (S). But the difference here was that I didn't rely on a single type of terrain. I used all the difficult going I could lay my hands on.
The last problem is what you do if the terrain dice are unfavourable and the Boundary either doesn't appear or ends up somewhere you can't use it? Hopefully you have a Plan B.
No, the idea of using terrain defensively like this doesn't appeal to me. It smacks too much of handing the initiative to the other guy, with little opportunity to put pressure on him. I always used the Aitolians aggressively - the terrain simply gave my fragile little Ps (S) the protection they needed to swarm around the flanks of enemy formations without being in much danger from mounted, while the heavier troops filled the gaps between the terrain features.
