OK, I have experience of neither commercial flying on a shift basis, or any experience of these two operators BUT I have experience of lots of different shift patterns and how they affect fatigue.
In my old job (ATC), fatigue is obviously a major thing to be avoided. We did a 4 on 2 off pattern, starting with a Late (4pm-10pm), then going to a Afternoon Swing (12pm-6pm), then Morning Swing (9am-1pm), then Morning (7am or 6am to 11am or 12pm).
This pattern allowed lots of recovery time and I was not in the slightest bit fatigued.
I also have experience of a 2 early, 2 late, 2 off shift pattern. This absolutely killed me, to the point where I went onto night shifts because the hours were better.
Possible explanation? Maybe someone on EZY, RYR or BAW can enlighten.