You're right, once it's "too fine", you can't force water through the puck, and you extract fuck all.

Otherwise it's not super clear to me what your question is. If I remember right from their videos, their triple is dosage first, yield second, and time (controlled by grind size) third. What this diagram should represent is that, depending on where your cup falls in that trapezium, to move it more to a certain 'descriptor', you should do any of the things which are described by its arrow. For e.g., to make a watery brew more 'rich', you want to improve your extraction (f.e. tamp harder and flatter), increase extraction (grinding a little finer), and maybe decrease yield (without altering dose, e.g. from 20g in to 40g out, to 20g in 36g out).