Reply from Stack Wallet: https://twitter.com/stack_wallet/status/1687457709225099264?s=20

"We are implementing border wallets as is. However we've also come up with a novel approach for border wallets. But there seems to be a misunderstanding, it doesn't utilize a grid at all. We're writing up a paper that will be available for public scrutiny. We'll be sure to tag you. :)"