Interesting chain of events... if no peers and Mail-via= Distribute, then
the mapping is pretty obvious (all of the list is in one place).
 
If peers, but no Distribute, it's not necessarily optimal distribution.
 
If peers and Mail-via= Distribute (is that valid?) it would do separate
distributes for the various peers (?).
 
Subscriptions would be routed based on peers, but the distribution might
come from somewhere else.
 
Thus, it would appear that the whole 'Peers=' business would primarily be
for purposes of subscription and list submissions.  It's semi-irrelevant
to the distribution, but could get tacky if it includes peers in the
distribution; there's a loop possibility hiding in there somewhere.