I'd hoped that my choice of words made it obvious that I was proffering advice and expressing a personal view based on experience, and most certainly was not attempting to state that "my" way was the only way. It clearly isn't.
Indeed, I tried to take pains to make that clear.
Failed again.
There will be as many ways of agreeing cost-sharing amongst groups members as there are Groups. (Or, more likely, as there are Group members). However, the way to reduce the potential for problems in the future, I am convinced, is to agree a philosophy from the outset as opposed to a hidebound process.
It's only an opinion!