[rancid] rancid "PAR" value only seems to do concurrent logins for a single device group?

[P C]

When you have multiple device groups (such as building1-switches,
building2-switches, etc.), I've noticed setting the "PAR" value has no
effect outside of an individual device group.  The script must run
through all devices in the device group it is processing before it
moves to the next group.  If you have many groups, and especially a
hung device in a group, this can take a very long time before it
proceeds.

Is there any way to make it run across groups?