I guess we can agree then that it's best if the Imperium doesn't have to find out whether 'nids can make the trip or not...
It sounds like a disaster waiting to happen... a single cruiser guarding such an important gate. You would think that since they cannot have a station set up on that side, that they would set up a massive blockade on the other side of it just in case.
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? Ultimately I think that´s up to the Gamemasters.