I think I saw that the RW paces are in odd numbered blocks at both starts. The sub 3 hours in pen 1, 8 minute milers (3:30) in pen 3, 9 minute miles (around 4 hours) pen 5 and so on.
Doesn't quite work out, as I thought there were 6 pace groups, but only 9 pens. But that must be a rough idea of what happens. Maybe walk run & 11 minutes milers are both in pen 9???