What is the respective weightage you normally give to historical incidents and fiction in your novels?
That's a tough one to answer, only because it depends how prominent the historical incidents, including the historical characters, are within the story and the level of historical learning the reader is forced to absorb. If the incidents are used as simply the background and parametres to the fictional plot, then it could be as low as five percent. But, if the story is based around historical events and uses or works in historical characters significant to it's plot, the weight of the historical incidents may be as high as seventy-five percent with the fiction being worked into it as twenty-five percent. I think any more than seventy-five percent and one is pretty-much writing non-fiction.
My Novel On Herring Cove Road uses a character driven plot set in the seventies in an actual place, so I am limited by the environment of the time (culture, technology, places, and etc.,) and there are no prominent figures used from that period within the story line. I would say that the historical incidents weigh in only at five percent and would not call it historical fiction, of course, being only forty years back does not, in my mind, qualify it as historical either, but genres can be at times pretty much subjective.
I have plans to write a fictional story based in the 1700's around indenturement. On my list of projects, and it comes in as the fifth novel. If that comes to light, historical incidents would be easily thirty percent as it would use characters from that time, based on actual events and the law and policies of indenturement and be worked with the parametres of the environment of the time period.