Flame size and its duration

What does the size of flame and its burn duration depend on?
The bigger outside area poi has the bigger flame it gives?
How can I influence how long itll burn? the more oil it soaks in, the longer it burns?
how about the shape?

I am asking this because I made myself new poi which are hollow inside and they dont have that big flane as I expexted and last only under 3 minutes if I spin faster(they are pretty big though) ...might the reason be thay they are hollow?

I want BIG flames... somwhat like spinner of deroit has

Bigger flame = shorter burn time, due to more fuel being used up.

With hollow poi, you'd be getting much hotter flames, cause there's more room for oxygen to enter the flames through the middle, which would cause the fuel to be used faster as well, cause it burns hotter/more used, etc.

Basically, I think SoD's are a series of ridiculously fancy knots or weaves, which means that they're not hollow, but they're actually quite tight (from what I remember from pics). I could be quite wrong on this though - best wait for SoD to correct it.