So if I understand you correctly, you're saying that damage to the wing/engine could be "forward flying splinters" allowed by the cone of Mick's simulation but the damage of the co-pilot chair could never be caused by any splinter of the fragment beam as suggested by AA or any other process during the crash?
Here's a merge of the AA suggested impact zone with a layout from this Austrian Airlines 777 200 seat map
as I could not find a more official cockpit floor map, not with a quick search anyway,
It goes too far to say that in this scenario the copilot seat never could have been hit at all by anything. It's unclear how exact the zone is or if there are any strays possible or which error margin or seat position range would be allowable to account for. Since everything is derived by AA from their photo observations, this kill zone cannot be presented as very exact either.
It would be fair to conclude the observed damage to the co-pilot chair does not necessarily exclude any scenario. What might count here would be the amount and direction of impact and exit holes (the Z scenario obviously causing more exit holes left from the cockpit considering the resulting vector of fragments). And the ability to verify if damage is really caused by HE fragments or something else.