I'm very interested in the details of its creation. How strong is the evidence of Kypros as the location of origin? And what alternative theories are there?

And what are some specific theories about the letter Qoppa? I've read something about how it could have been the labiovelar series from Linear B, and even more amazingly that Phi was purposefully fashioned out of that letter from a conscious understanding of having evolved from that sound. How good is the evidence for such a claim, and are there any more detailed resources than the few vague mentions I can find online? According to this article, the Greek in Kypros was essentially a direct descendent of the Mykenaean Greeks who used Linear B. So could the Q- series have been preserved and/or remembered long enough for them to assign that value to Qoppa 400 years later? On the other hand, the absence of that series in the Kypriot syllabary with seemingly no problems using the evolved values (P- series) looks like evidence against such an idea. And I frequently read about how Qoppa is thought to be distinguished from Kappa by the back vowels, but this doesn't make any sense at all to me (I mean from the perspective of the people developing the alphabet; the eventual usage of such arbitrary spelling rules was clear). Why would the K sound be singled out as being different with back vowels, unlike the G, or any other sound? If that was the case, then Sigma and San should have similarly been differentiated by some trivial vowel class distinction. Instead, it seems to make more sense to me that it's the labialized nature of those two vowels (O, U) that make the consonant distinct from the K. This seems like evidence of some sort of memory of an old phonemic distinction, especially considering that the more useful distinction of aspirated velar (Xi) was being passed over. And perhaps the fact that the aspirated distinction had no literary history while labiovelar did can explain this.

As for the sibilant letter confusion, I have a personal hypothesis that I really like, but I wonder if it's a good idea or if I'm just missing something obvious that makes the more common confusion theories more sound. My idea is that there was some sort of effort to put similarly named letters together, possibly for convenience or aesthetics. So for example, Sade (Zeta) fit well before Heta Theta Iota, while the Zayin it replaced fit better with Mem Nun (Samek) 'ayin, which seemed to undergo some sort of final nasal deletion after Hellenisation: Mu Nu Ksei Oi. I've read that "shan" was a possible pronunciation for Shin (I'm really interested in some evidence for this), which would explain the names of the final two sibilants San and Sigma (from Samek of course), and their eventual identical value and consequent name confusion by the various dialects explains their position.