With all the speculation hereabouts, I offer this (gift) article in the Washington Post, which is the best I have seen thus far. It has several drawings showing the sight lines of both the shooter and the Secret Service snipers, along with other relevant details. It also includes things like: the building the shooter was on was outside the perimeter zone controlled by the Secret Service and was left to the management of local police. (In hindsight, obviously a mistake.)

I also learned that the “sloped roof” the shooter was on was actually a pitched roof, and he clambered up the side that was invisible from the snipers’ positions. Their view of that building was also hampered by trees, though it wasn’t totally obscured.

And there is a citizen video of the guy crab walking up the slope of the building towards the peak just a few seconds before he opened fire.

It’s the best explanation I have found thus far, and it’s here:

https://wapo.st/3Lwyt6k