Account and System Management : System Management : Global Settings : Setting HTTPS Payloads

Setting HTTPS Payloads
By default, Metasploit communicates over a standard TCP connection with SSL. HTTPS payloads provide you with some level of stealth, but the payloads may not be as reliable as HTTP payloads. This configuration generally works well in most cases, but if the target is behind a proxy, the proxy may not be able to handle the SSL connection properly. If you know that the target is behind a proxy, you should not use HTTPS payloads. You should use HTTP payloads instead.
If you want Metasploit Pro to always try to encrypt the HTTP connection, you can set it to use HTTPS based payloads.
1.)
Choose Administration > Global Settings from the main menu.
2.)
Choose payload_prefer_https from the Global Settings.
3.)