Indeed, Dave, d'accord.
However, I was endeavouring to provide a reasonably simple explanation for the OP and one relevant to his/her stage of learning. I noted the need to consider all three controls (eg the HS125 Va) but didn't see a necessity to provide too much detail at this stage lest I confused more than assisted.
Had I been talking to engineers, my response would have been somewhat different.
However, hopefully. some of the folks do chase up some of the references you have provided.