Subordinate conjunction "Just as": different meaning depending on the position in the sentence?

I was searching for sentences with just as in the meaning of "in the same way as".
It seems to me that subordinate sentences with just as can either describe ‘the way’ something is being done (a), or providing a comparison with a ‘similar situation’ (b):
(a) He’s signing his name just as he’s always done it. (https://www.dictionary.com/browse/just-as)
(b) Just as an adjective can describe a noun, an adverb can describe a verb.

The above examples, as I see it, show that just as can "focus" on different aspects of a situation. What would be the correct explanation of the difference?

Also, it seems that in the case of (a), the sentence with just as can’t proceed the main one (*‘Just as he’s always done it, he’s signing his name.‘) unless we mean not the way he signs his name but have some specific context (like referring to the fact that ‘he has signed his name before, he is signing his name at this moment, as well.’)
Whereas (b) seems to allow such a modification without changing the meaning:
(c) ?An adverb can describe a verb, just as an adjective can describe a noun.

How can it be explained? Would it be true to say that when at the beginning of the sentence subordinate sentences with just as can modify how smth is done but not compare two different situations? And when used after the main sentence it can have both meanings?

Other examples are:
(d) comparison of situations:
Just as Jack abandoned his family for an adventure, John left his wife and went to sea.
John left his wife and went to sea, just as Jack abandoned his family for an adventure.

(e) in the same way as:
I wrote my essay with five paragraphs just as my professor told me to do in the instructions. (https://www.myenglishteacher.eu/blog/subordinating-conjunctions/)
?Just as my professor told me to do in the instructions I wrote my essay with five paragraphs.

I would be very grateful for any information on this matter.