Why must -N be >= 16?

Just trying to start up a 'mini-process' of -B 8 -N 4, and it tells me
that -N  must be >= 16 ... why?  

documentation doesn't seem to imply/indicate this, should it?
      -N n_backends           n_backends is the maximum number  of  backend  server           processes  that  this
postmasteris allowed to start.           In the stock configuration, this  value  defaults  to           32,  and  can
be set as high as 1024 if your system           will support that many processes.  Both  the  default           and
upper limit values can be altered when building           Postgres (see src/include/config.h).
 

For security reasons, I have a server running on its own port, and I want
to restrict the amount of shared memory that it uses, and I know the app
will never open more then 4 backends (it would be lucky to hit 2), so
figured 8/4 would be nice and safe...

Thanks...

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org 
primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org