I have never been sold on EMG methodology. I think it's a simplistic approach and gives more questions than it purports to answer. Yes, I can see the pectoralis minor being more involved in an incline but it's a relatively minor muscle and it's not isolated to the upper chest. Most bro science thinks there is an upper pec muscle and central pec muscle. No, there is one pec with a minor diagonal muscle called the pectoralis minor going across the the entire pec region.
I do not know enough about emg to make a substantial rebuttal. But doesn't the text i showed say exactly that, that the minor ISN'T more involved during an incline.
I do know inner chest cannot be targeted, because a fiber fires at 100% or not at all (Rather the number of fibers) and seeing as the fibers are crossed horizontal the inner chest cannot be trained. B
I always thought the number or the location (even if the chest were 1 muscle not 100% of the muscle will fire when not needed) of the fibers contracting would be different when on a small incline. (Or any other angle) But the most musclular recruitment can indeed be seen with the decline.
So i am definitely not disagreeing with you, i'm saying i don't know for sure and that is a fair point to take.
I do always train my upper chest only on a slight incline, like only 1 step during incline dumbell, because i feel it works the shoulder too much when i increase the incline.