ssh reverse tunneling: cannot set up for web access?

I am trying to set up web access through NAT using ssh reversing tunneling. Suppose A is a public machine outside NAT which I can use for tunneling, and B is the real web server inside NAT.

On B, I do

ssh -N -R A:5700:localhost:443 user@A

So basically, I forward "A:5700" to 443 on B (https).

On A, I successfully visit B by URL "https://localhost:5700".

However, I cannot use A's address like "https://A:5700" even on A, which means I cannot give this URL to other people to let them visit B.

Any steps I miss here to set up this kind of proxy?

Thank you very much for the help.

More,

When I test with

$ telnet localhost 5700

it is good, but not "telnet A 5700" (Connection refused). I check iptables and the port is allowed.