The group worked together and wrecked their heads trying to solve that issue together. While they could help Iori, they couldn't since he could use the extra mana to strengthen himself, or he could lie about the necessary amounts of mana necessary to keep his domain active as the vessel increased.
Solving that issue had been a massive pain in the ass, but it didn't last more than one week since everyone worked on it together. First of all, Rain rebuilt the Meditation Rings, this time with Maxime's help, and that triplicated their effectiveness.