Improve Outlook Instant Search for archived items

Today, Instant Search (Outlook integrated search) is only searching the metadata cache (mdc) for archived items. The problem is that if we search for a word at the end of a message, there isn't any chance for this message to be retrieved. The same behavior accurs if there are many recipient (not so many in fact).

It would be very helpful that Instant Search could be able to search the whole items including full body, attachments, etc... and not only the metadata cache. Windows Desktop Search is able to search the whole item and retrieve them, why not Instant Search?

Thanks!