I've only dabbled with these and not enough to have any informative experience to share. However, I've thought that the classic fire hole, that is actually two holes joined by a "tunnel" might be slightly improved upon by adapting the prairie dog tunnel as a model.
The P dog tunnel has one opening mounded up and a second that is not. It's opening is exactly at ground level. Wind blowing over the mounded hole causes a draft of fresh air to be drawn in from the lower hole. A Dakota fire hole built with the burning hole mounded up using dirt taken from the hole, with the air intake hole remaining flush with ground level might burn even hotter that a fire hole on which both the holes are at ground level, providing there is some wind of course.
The Dakota Fire Hole has been describe in US Army survival manuals going way back.