@Donald-And-Mary-Ann0 There isn't one. What a lot of hosts are trying to do is make their place affordable to small groups as well as making more money from large groups.
A better way is to have 2 listings - Say a 4 bed listing for 8 people and a 2 bed for 4 people. Locking off 2 bedrooms reduces the cleaning/wear and tear and this concept also allows blocking of the 2 bed listing in high season when you want to book the larger property.
Hi @Donald-And-Mary-Ann0, Did you get a chance to read the suggestions from our lovely hosts? I'm also sharing an article 🔗here on how to add this fee, in case you find it useful.