need help with SSH through firewall

does anyone have any experience with punching through a firewall using something like corkscrew and SSH? Here's a description of my problem:

I'm trying to punch through a firewall, on port 443. I'm
running CYGWIN. I've tried OpenSSH 3.8.1p1. There is an HTTP Proxy.
I'm using the Proxycommand along with the proper arguments. I've tried
connect.c, corkscrew and proxytunnel.

I can get a successful handshake with the proxy server (I get the
connection established). But I get an immediate FIN packet from the
sshd. In the sshd logs, I always get "Did not receive identification
string from XXX.XXX.XXX.XXX"

Here are my questions:

1) Quite possibly the proxy server is somehow disallowing this,
although I tend to think not. The reason I think not is, I can use
cURL successfully and get this back from a request to
https://my.server.address

curl: (35) SSL: error:00000000:lib(0):func(0):reason(0)

Anyway, how can I tell what http proxy server is being used, to do
more research into whether or not it is squashing the request somehow?

2) What exactly is the "identification string" that sshd is expecting
and not seeing?

Any ideas/pointers/suggestions would be much appreciated.

Also, if more info is needed please advise.

Thanks in advance.