ssh over WAN: TCP window too small

[Chris Stankevitz]

Hi,

# cat /dev/urandom | ssh root at host 'cat > /dev/null'

I use the above ssh command over a high-BDP WAN link (80 ms @ 100 Mbps). 
  tcpdump shows I am TCP window limited to 64 KBytes (yielding 5 Mbps). 
  iperf with default options gets the window opened to 500 KBytes 
(yielding 35 Mbps).

Both sides of the connection: FreeBSD 10.1 w/default sshd options 
(except I permit root login).  In particular, HPN is not disabled.

Can anyone explain my abysmally small TCP window?

Can anyone recommend some tools/tricks to figure out what in FreeBSD 
and/or base SSH is limiting the send/recv buffer and/or TCP window?

Thank you,

Chris