The key thing about a land value tax is that it's based on land value, and not land area, so the allowance should also be based on value and not area, for it to

The key thing about a land value tax is that it's based on land value, and not land area, so the allowance should also be based on value and not area, for it to work right. 10,000 sq ft in Manhattan is much more valuable than 10,000 sq ft in a rural area, and so it doesn't make sense that both should be treated equally.