Thank you for your reply. I did not perceive disrespect to Dr Ishaq, one has the right to agree/disagree with a phonetic theory irrespective of respect.
01. Djandja/Gshima are two of the most problematic letters when it comes to pronunciation. So, for these letters I really cannot argue much, the only argument that was intriguing is that the GB rule for pronouncing it seemed reminiscent of the way the English G is pronounced.02. For educational purposes in schools, usually a letter is assigned one phonetic value then, as the student learns other values are grasped e.g. in school books in English S is given the value of S as in sit. In reality, S is pronounced as S as in sit, S as in sun (slightly different, closer to Arabic Sad), Z as in as, J as in vision, invasion, Sh as in sugar, sure, or silent as in island. My bet is that for educational purpose hori was equated with its most common pronunciation h however, there are a few words where it still exists as the arabic ha e.g. tobh, timsah, handous, honfa, hantour03. The Chi letter is also tricky as in Greek it has a different pronunciation, so, Copts were using a process of approximation to imitate the sound, this could vary from a person to a person, this may explain the variability.
Having said that, I see that the main purpose of the language is communication, I do not think that these would affect mutual comprehensibility massively. So, by all means, if Sobhy's pronunciation scheme is what you believe is more authentic, please feel to use it.