I want to know the reason for all the different pronunciations of the prefix en- in English words. For example, words like enable, enlarge and endure have the prefix pronounced as /ɪn/, at least according to wiktionary. On the other hand, the word endanger has it pronounced as /ən/. There are also some words that can apparently have it pronounced as both, such as entire. Additionally, there are words like enhance, engage and enjoy, which can have it pronounced as /ɛn/ as well.
I thought the pronunciation of the prefix might depend on the etymology of these words, but they all seem to be derived from French. Is there an underlying hidden rule for the different pronunciations or is the pronunciation simply arbitrary?
Note: I am aware that certain words have retained the French pronunciation with /ɑn/ or /ɒn/ in GA and RP, respectively, such as the word entrepreneur. However, such words are not that common and I'm not interested in them for the purposes of this question.