Safari seems not sending If-Modified-Since header for main address

Not sure I'm in the appropriate forum but let's try (if there is more appropriate one please advise).

When Safari requests a resource (page, image...) to a web server it doesn't provide If-Modified-Since header for the main resource of the request. That means the web server can't answer "resource not modified, use your cache". This is not the behavior of other browsers and not good in terms of performance for the web server as well as for the user.

However Safari sends this If-Modified-Since for the sub-elements of the resource (e.g. images, css in a page...). Which is good.

Is there a way to influence Safari's behavior to provide a If-Modified-Since for the main resource requested to the server?

acama,