You'll never find a coffee brewer that measures a true 8 ounces for a cup.
When people used to drink coffee in dainty cups and saucers, those little cups only held 4 or 6 ounces. A cup of coffee was never a full 8 ounce cup.
Some coffee makers use the 6 ounce cup as a measure and some use a 4 ounce cup. (And some seem to randomly place the cup markings on the sides of the coffee makers)
That's why it's safer to use a standard measuring cup to measure the amount of water you want to use and then adjust the amount of coffee you use.....and once you get it the way you like it, keep doing it the same way and you'll be fine.
Rose