Sorry, but the title is rather confusing. The OP is complaining about the amount that he was given and someone else says that the glasses are too small. I know for a fact that this has been a discussion point on several occasions. I suspect that they had or are loading less pre-departure Champagne as it is Duty Paid. I'm just hazarding a guess here. What does surprise me is that the OP did not ask for another one - I would. It also surprises me that people - and this is not directed at the OP in particular that have been around for years - are particularly reticent in real life but have plenty to say in cyberland.

I am thankful that BA serve perfectly adequate glasses and are not slopping everything into tumblers on the basis that quantity matters more than quality. Whether they are using Champagne or English Methode Champenoise I have no idea but intend to find out. I would add that the PDBs are served in glass as opposed to plastic over at American.