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.
Always Be Training
Training does not stop over the lifetime of any staff. That is our only competitive advantage.