This is mostly for compressed bamboo. Each bamboo can burn for 0.25 items, and it's crafted 9 to a block, which should be 2.25, but it's 1.25. And if you go for Vanilla mechanics logic, it should be 2.5 or 3 even, because something like coal can be compressed to be 10x instead of 9x burn time. As it is, it's not only not the same math, it's a loss to use it as fuel.

I noticed this when I was trying to farm Bamboo for Endoflame fuel.