A problem here is that there are times when practically everything written on a given topic is wrong.
As I’m sure most would agree, there are many things known today that are the opposite of what was universally or virtually universally thought correct at some past time, even maybe just 10 or 20 years ago.
At that time, practically everything one could have read on it would be wrong.
This is one of those things.
The problem is that the correlative fact, of higher SHBG meaning, for same total testosterone, that there is less free T, and vice-versa, as total T is so to speak the product of free T and amount of SHBG, is so persuasive. And furthermore that it’s clinically useful to note for example that, well, at first the total T for this woman wouldn’t be alarming, but look how low her SHBG is: and sure enough she has symptoms of excess androgen.
Again it’s correlative. Doesn’t at all mean that the low SHBG caused the condition, but rather, since total T is so to speak the product of free T and amount of SHBG, yes of course for the given amount of total T, if the SHBG is low then the free T had to have been high for that total to be achieved.
So that’s persuasive for people, though it doesn’t prove or even remotely show causation.
I expect you’ll find lots of stuff that will just confuse it further for you. Short of studying the general matters involved with equilibria, receptors, protein binding, etc and applying it to the problem, I rather suspect you won’t find reading material that will help you on this one.
Try the calculation for yourself though.
A lot of times, people doing something for themselves “lights the bulb” in a way that explanations from others cannot.