It's not possible to use Tor behind a http-only proxy (not supporting the "connect" method.
Tor will make all its directory requests through this host:port (or host:80 if port is not specified), rather than connecting directly to any directory servers.
Tor will make all its OR (SSL) connections through this host:port (or host:443 if port is not specified), via HTTP CONNECT rather than connecting directly to servers. You may want to set FascistFirewall to restrict the set of ports you might try to connect to, if your HTTPS proxy only allows connecting to certain ports.
When one is only using HTTPSProxy, will also directory requests get routed through that proxy?
When one's goal is to route all of Tor's traffic through that proxy is it required to use HTTPProxy and HTTPSProxy or is using HTTPSProxy alone sufficient?