Mine does the same. When I make a 180ml bottle it turns out as 210ml with formula. I did the same as above comment and ran the machine without formula and it was 180ml. I asked the HV and she said if he finishes the bottle it's still 180ml
We use the prep machine and our little girl is on 5oz and also use the mam bottles. It’s totally fine. It is correct, it’s just the volume of the formula and water mixed together that makes it do that
Its the volume of the formula, our did the same, we tested it by making a bottle but without the formula and it was correct