After talking to a lot of trainees, it seems like many of still can't differentiate between (A: "sweeter" vs "less bitter"), differentiate between (B: "there is X amount of bitter stuff in solution, and Y sugar" vs "there is X, and [Y+Z] sugar" where Z is a positive quantity), and differentiate between A and B.
B refers to noumena, or objects in an absolute sense. A refers to phenomena, or your perception of objects. A and B are different because this thing called our brain chooses to ignore a subset of available information at any time - the subset changes based on how you train your brain/body, and how your nerves and all that. (Example: if your left hand is being hit with a hammer, you will probably not realise if your right hand is being tickled - unless you have practiced to notice both at once.)
Back to coffee. You need to understand the physics/chemistry of cooking in order to get the model of how your machine settings are affecting B in the cup. But your main access to B is via A, and that is why you need to study how your brain is processing the difference between B and A.
You can start by making yourself a bitter drink, 100ml, and tasting it. Then add a pinch of sugar, stir till dissolved, and taste again. Repeat step 2 a few times. Record the level of perceived bitterness / sweetness every time you retaste the cup.
This will help discussions during daily calibration.
Training does not stop over the lifetime of any staff. That is our only competitive advantage.