The Plus Rule makes sense to me, and I've seen various online explanations that fit with how I understand it. But in play against King Elmer, it seems to be rather erratic.

Example 1 -

The Dodo card is in the bottom right-hand corner, the Godbert Manderville card is directly above it, and the Cactuar card is played in the center of the board (i.e. to the immediate left of the Manderville card). These are the only cards on the board. The total of the cards on the left side of the Manderville card is 9. And the total of the cards on the bottom side of the Manderville card is 9. The Plus rule doesn't kick in.

Example 2 -

The three cards involved this time are the Manderville card in the center, the Garuda card in the center right spot, and the Bahamut card in the bottom right corner. The total for the Manderville and Garuda cards is 13. And the total for the Garuda and Bahamut card is 10. The Plus rule *does* kick in this time.

According to my understanding of the rule, it should have applied in example 1, but did not. And it shouldn't have applied in example 2, but did. What am I misunderstanding?