Vhere, Sh’A O’Ch 170:8, Ashkenazim allow for the cup size.
But a fair point: Beitza 25 proves a general klal on derech eretz min haTorah – I don’t think anyone argues on that. Pratim are obviously culture-dependent (and some commentaries say – upon health and size of the person). We don’t leave food on a side of a plate for the waiter to eat, and (in America) are not careful about using appropriate utensils as Victorians did. So, you will have to ask your local Rav.
What I do not understand – do we judge by general culture of the times? by the observant community? your own corner? Does it depend who of the above will see you?