The principle is simple: transitioning between planes shouldn't divide the template structure into two parts, unless it's a feature of the structure itself, like in h3dm1, for example. That is, the transition to another plane during the game should happen as early as possible.
I think the same mirrored Diamond could have been made with two transitions to another plane from the starting zone, but instead, there's only one transition, and for some reason, the guard on it is stronger than the guards within the same plane.

I believe that in the future, a software mechanism will be implemented for mirrored maps to prevent transitioning to the opponent's plane before day 121. This will solve the problem of early contact. Experience has shown that even with replaying the turn, this can be fatal for the blue player.

Therefore, on the mirrored Diamond, I specifically placed a slightly stronger guard at the teleport spawn point – so that people would primarily rush into the zones of their own plane, and not get used to the idea that they can freely enter the opponent's plane in the first week.