James Mitchner fairly leaps to mind. I first became acquainted with him while reading Hawaii as I relaxed on Waikiki Beach during R&R from the Vietnam War. The insights that I gained from that novel helped me more abundantly enjoy the almost five years I lived in Hawaii following my tour of duty in Vietnam. However, I believe that The Source was Mitchner's greatest work. It provided even greater insights into the nature of the people living in the Middle East; insights that are invaluable in deciphering current events there.
Some may not agree that the Camolud series by Jack Whyte is historical fiction. Although they may argue that his interpretation of the legend of King Arthur is pure fiction, I believe that he is true to the milieu of time and place; Britain at the time the Roman Empire is contracting and the legions quit the nascent island nation. I cannot imagine anyone more accurately nor more interestingly portraying this period of history, than to imagine Roman equestrians who remain behind to attempt to build a unified nation on the ruins of a crumbling empire.
Unfortunately, there is a flaw in Twain's concept; it only works if there are good journalists to record history as it unfolds. There may be some out there today, but I haven't seen them. Some argue that a bad thing happened during the Vietnam War; journalists became performers vying for popularity ratings on television screens as news became a profit center in the broadcast industry, and political correctness drew larger audiences than factual correctness.
The degradation of the journalistic profession continued as this philosophy found its way into universities. Whereas journalists had traditionally worked their way up the ranks of the newspaper business learning their craft along the way, modern journalists graduated from institutions that shielded their students from reality and exposed them to the progressive philosophy. Indeed, journalism professors became ring leaders using their students to bully anyone who dared stray from their chosen views of society and social order. Thus, the product of modern journalism may seem well-crafted, but it is hardly to be trusted as the foundation for understanding the milieu or the characters of any stories that are their subjects.
All things considered, I will continue reading historical fiction (and writing it). Hopefully, I will remain true to my story and people will find it insightful as well as entertaining.