Hey @x_jdj_x,
Both yes and no. You are correct that once in that zone the value of traversing the area is the same, though the AI will actively seek the shortest path to the lower value of the zones it can traverse. There are also Entry costs that you can set as well which are one directional (enter not exit). You can also use those to set barriers, although the travel cost may do you better.
In short, if your hill is highlighted in a higher travel cost and your lower height area is next to it, your AI should in theory actively seek a lower zone next to it if available.
You can still change these factors with multiple queries set at runtime as well.
I hope the above helps guide you toward the solution you are looking for!