Tomas, your analysis is on the spot. Well done!

In other words, it all boils down to the facilitation of the articulation.

How?

Arabic letters are divided into soft and hard letters (like in Russian, except in Russian it’s the consonants that are divided and not all the letters):

Since we’re talking specifically about the ا:

This rule makes sense, because, as you explained, why make it hard, when it’s anatomically easier to pronounce it soft, and make soft when it’s easier to make it hard? The letter ا itself is neutral; neither soft nor hard. Its articulation, hard or soft, is decided upon by the letter preceding it.

Yeah, I'd love to read your take on that!

I understand it the following way:

ظابط cannot be pronounced zhääbit, because of the guttural nature of ظ

It simply does not allow your tongue to form the ää, because it's needed for your ظ

I'd even say, that when pronouncing ظابط the Alif almost sounds like an Å?

My question: Could one make a rule of thumb out of it: After guttural sounds it's an ÅÅ, whereas any other time it's ÄÄ?

For example

صاحب ساحر

9åå7ib sää7ir ?

Andrew, if I understood your question correctly, you’re wondering why for example the alif in باب is pronounced more like the German ä, while the alif in ظابط more like the German a. Am I right?

This is interesting, as far as spelling is concerned. Regarding pronunciation, I have never found a good explanation of how long and short vowels are affected by their phonetic context in Arabic and of how they are rendered accordingly. I clarify with an example: the alif in باب does not sound like in ظابط or in قابل. While I realise accents can vary in different varieties of Arabic, this is a point that most textbooks neglect when presenting the ABC of the language.