Encounter Areas Running Together

I’m designing an intro adventure, and it’s taking place beneath a ruined hill-fort. The hill-fort itself, like most fortifications, is designed to have interlocking defenses–when attackers are dealing with one problem, defenders in the next are probably aware of the attack and responding.

It’s based on a motte-and-bailey design, so for example there’s a palisade (somewhat dilapidated) surrounding the lower bailey, and a ditch/moat around that. Plenty of ways for an adventurer to deal with that, but the bailey it’s around is inhabited, and the inhabitants are likely to observe their approach. My first thought was that the ditch/palisade should be one or more encounters, and then the bailey, but is that reasonable? The whole point of the design is that while somebody’s fording the ditch/climbing the palisade the guys inside are stabbing them with spears or shooting arrows at them.

Would it make more sense to use these things as added Ob to a Kill or Drive Off conflict? (That’s assuming that’s the approach the adventurers take; others are perfectly reasonable as well.)