So the trigger area is supposed to stop the movement of the first corps over the line, but then let the rest through? OK, but I'm not sure I understand why. In the boardgame, there was some point to stopping only the *last* corps or two, because you could fight them right away on their own. But if you're putting down the corps in reinforcement, you can't do that.
You could if Austria were moving first in the land phase, but most likely invaders will be able to restack before Austria moves. Russia and Turkey move earlier, and France can.
However, if this is the way you meant it to operate, and it's not buggy, I guess the question of whether it could be improved is not top priority.