The solution? Smaller glasses of course. Complaints dropped to zero.
Sadly, wanting good things leads to a lot of stress, at least in the US. (Go to Target sometime. Is there anything there that you couldn't get a higher-quality version of on Amazon for less money? Nope.)
Expectations? If you put a big cup in front of me, I can expect you to fill half of it, fill it completely or anything in-between. If the glass is small, I expect you to fill it to the top, no uncertainty.