If you were confident that additional investment won’t let you pick something you favor over AMF, or (with larger or staged lotteries) fund a new project you would fund over AMF, then you believe you have constant returns to donation budget over the relevant range. So you wouldn’t expect to do extra good.
Most of the reasons for increasing expected returns with donation budget (to take more time to make a better decision in a minority of world-states, to open up new opportunities, to make it worthwhile for charities to spend more time answering your questions) involve the possibility of something more complex.
So I’m guessing the idea is that donors will do something a bit more complex than just throwing the money over to AMF?
If you were confident that additional investment won’t let you pick something you favor over AMF, or (with larger or staged lotteries) fund a new project you would fund over AMF, then you believe you have constant returns to donation budget over the relevant range. So you wouldn’t expect to do extra good.
Most of the reasons for increasing expected returns with donation budget (to take more time to make a better decision in a minority of world-states, to open up new opportunities, to make it worthwhile for charities to spend more time answering your questions) involve the possibility of something more complex.