nice work with the mock-up 
what just came to my mind here is the Higgins Preliminary Report. There he states:
“Shot 9 hit Crooks’ rifle stock and fragged his face/neck/right shoulder area from the stock breaking up.”
and further
“I believe the shot damaged the buffer tube on Crooks’AR. I won’t be certain of this until I can examine Crooks’ rifle, but I’m 99% sure, based upon reliable eye-witness ESU tactical officers who observed Crooks’ rifle before the FBI harvested it as evidence.”
Assuming his observations are correct, that somehow would rather support he first shot 3 rounds from a rearward/down position and then moved slightly to a forward/up position to release shot 4-8. There was a gap of about 2.8sec between shot 3 and 4, that would be enough to move something like 1.5 feet forward/up. He would then also be more exposed so the SWAT guy could see him better and take his shot 9.
Also Trump ducked down quite quick after shot 3 (about 1.5sec). Maybe Crooks couldn’t see his target anymore and therefore moved forward and a bit up to see better where to aim. And because he couldn’t make out Trumps red Cap anymore he went into kind of burst mode and released shot 4-8 pretty fast.
I’m not sure but would the spread of the ejected casings likely be bigger in case of fast fire? So maybe casings of shots 1-3 and 2 of shots 4-8 landed north roof side, and 3 of shots 4-8 landed south roof side.