The rules don't have a clear definition of "penetration," so it's unclear what you're basing your statement on when you say there's no penetration into the zone. And this definitely needs to be clarified in the rules.
Also, it's unclear why the shortest path is relevant. The rules don't require attacking a Guardian of the Gate (GOTG) via the shortest path; there are other criteria.
By the way, as an alternative, you could allow stepping onto the adjacent territory by 1-2-3 cells maximum, either by moving past the shifted guard or by flying, but only with the purpose of:
1. visiting an object or resource belonging to your zone
2. attacking another shifted guard at that passage.
