I don't think it affects it, but it must be tedious to play like that. People that want to optimize citizens growth usually put cities on focus production and lock the proper needed food tiles manually once and for good unless they get to negative happiness which in such a case they reset tile assignments in every city, which I find tedious also. I generally think it does not worth the hassle just to spare 1 citizen 1 turn production. (I do it early though, or try to do it)
But I do think that, since the food basket grows with every new citizen so that it might theoretically be longer to grow the next citizen after that, that the aqueduct fulfills 40% of the new food basket (the green bar if you want) a new citizen places at birth, regardless of the amount of food you had before citizen growth.