what happens is that there is a long chain of function calls, object create and method calls that eventually end up at
WP_Http::_get_first_available_transport in file wp-includes/class-http.php
This function calls other function that determine what transport method is used based on what is available on your server.
The order of the check can be altered. this method includes this line
$request_order = apply_filters( 'http_api_transports', array( 'curl', 'streams' ), $args, $url );
so WP first checks for CURL and then STREAMS. By default, if you have CURL available I would say that’s what is used. You could create a filter to reverse the order of these and try for STREAMS first?
There are other possibilities as well, not sure if they are of any use in this situation. Search the file wp-includes/class-http.php for “class WP_Http_” to find them all.
