Let the players set a maximum amount of land for them to take from another player.

Country A hits Country B and sets a max land take of 1500 acres. The formulas say that Country A gets 2000 acres. The idea would be that Country A would get 1500 acres and the ghost acres associated with a 1500 acre LG.

Self farm and Land Trades?

You could calculate it yourself :P

grabbers wouldn't use that since they want as much as possible.

And what advantage would country A receive from choosing not to receive full gains from their attack?

This would be more used for Retals where L:L has been granted.

some alliances might use it but some take more retals even if they are only 100 ish acres short of land got back.