I think it makes sense. So if you have clean reports little changes can effect your score in a greater way.
Yes. In a greater way that the same change in UTIL would if you were in a negative scoring bucket.
Could a 1% change in UTIL alone account for a 15 point change? Maybe not. It would seem to me that something aged too.
Does having the Amex charge card help scoring?
Perhaps so. What cc's did you have before you added these two?
Nord V 4k
Macy's 8.3k(has not reported new CL)
Wave CU 3k
Credit One 750
6K(My mom did this to get my credit started)
And One Installment loan
That is the basically what is on my credit report.