Dear Starbucks

I buy a breakfast combo at sungshan store , the clerk is kind enough to ask if I want to " upgrade " my latte from middle to large , I say " please "
The bill is 200 in total , kind of expensive so I ask if I am buying the morning breakfast package? He said yes and I point to the menu and show him " the package with middle cup is 150 , how come upgrade to large is 200 ? "
My following question is : if I buy one middle is how much : 120 he said ,.ana large ? 135 ,,it's only 15 NT different but when they ask you to upgrade your coffee , they change you 35 NT more , it don't make any sense .. right ? I didn't ask for anything but to explain to the clerk he should remind customer the price difference before charges them .
I don't really get it .


Roger