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I think it's best to start with templates, not Castles. The fewer zones on the map and the smaller the map itself, the easier it is to find the Grail. For example, on Jebus, if you find it in the first week, it will significantly impact the game. And in the case of these templates, the question arises: why should the Tower and Conflux be disadvantaged? What if I don't have any other cities? The Tower isn't a strong Castle anyway, so let it have this advantage. Another option could be: if a player places a Grail in a Tower, they must inform their opponent about it on the same day, and from that moment on, the Cartographer can be used. (It's a bit complicated, but fixing the weak Tower isn't the right approach.)
A Grail in a Conflux, on the other hand, is an excellent solution to the constant struggle of finding control.
In general, I see the Grail as a way to add variety to the game. If an opponent is putting pressure on you, you dig up a Grail and place it, even if it's in a Swamp; stats increase by 10, and you have a chance to fight back, especially against Shackles and the like. But what if I don't have a Swamp, but I do have a Tower and a Conflux? And again, there's no variety.
But digging it up with 111 – I'm against that. The fewer zones, the higher the probability that the Grail will be in your starting zone. In the first week, there are usually more free moves, but by the third or fourth week, the chains are tight, and all heroes are needed. That is, if you repel a couple of Obelisks and realize that the Grail is in your zone, it's not difficult to dig it up in the first week. On HotA, the probability is lower, but it remains. And a Grail dug up in the first week will simply decide the game.