I have a question in my mind as I (bow) saw my timber logs.

It is " what is the ideal thickness of branch to cut so as to maximise the output of burning timber from my logs?" (I have a choice if thicknesses I can cut.( at what point for example do I say that this twig is just too small to bother with)

The variables must, I suppose include the density of the wood, the sharpness of the blade, the strength and endurance of the operator, the weight of the bow saw,the speed of the sawing action, the angle of cut (a separate question that: what is the ideal angle?) etc etc...

To my mind this seems like too many variables to be used to make up a solvable equation but what would be the best approximation?

Obviously I can work it out by weighing an identical time period of output from logs of differing diameters but would be interested if there was a usable equation to cover this circumstance
thanks in advance