I did this research as a Clinical Hypnotist* 12 years before Mack.
* I used to call myself a Hypotherapist until a friend of mine hyphenated the title as Hypno-the-Rapist.

My conclusion was that the phenomenon was real but the encounters were not with flesh and blood entities.

You may already know that I was close to Allen Hynek.
Unfortunately, by the time I made his acqauintence he had already learned he was dying of a very rapid and rare brain tumor. His wife kept his spirits up and pressed him to continue his work. His most proud moment at that time was his paper he was going to present to the American Academy of Sciences. He showed me the work. Primarily it was a another catagorization of kinds of unusual craft akin to his original catgorization of encounters.
Most people know him for establishing the term 'close encounters'.
He was a very kind, honest and forthcoming man.