Charging more for less, and less for more

There is this coffee shop near me that makes good coffee and provides a nice environment for doing some work. The other day I ordered a small iced latte with less ice.

Oops, I forgot about their $0.75 fee for "less ice". The small drink rings up to $6.80. It's $5.50 for the hot latte, $0.50 extra for ice, and $0.75 extra for less ice.

One time, I asked them why they charge more for less ice. They said less ice means they have to give me more coffee.

I don't know why that sounded sensible at the time. Because it doesn't make sense.

I should have asked them why they charge $0.50 for ice in the first place. By their own logic, the iced coffee has less coffee than the hot coffee, thus shouldn't there be a deduction for making it iced?