Don't put the flaming rag down an open bottle filled with fuel. Instead, fill it with fuel, close the bottle, and tie the rag around it so you won't send flames everywhere, only your target
Same energy as a YouTube comment I read on a War Thunder video that said, "The thermite mixture is a combination of finely powdered aluminum and iron(III) oxide (also called ferric oxide) in a mass ratio of 1:3 respectively, a 5-7.5cm length of fireworks sparkler."
Alternatively, magnesium shavings can be used in place of a sparkler for ignition. You can also reduce the ignition temperature by adding powdered magnesium on top or mixing it in up to 10%.
"I'm telling you, Molotov cocktails work! Any time I had a problem and I threw a Molotov cocktail, boom! Right away I had a different problem." -Jason Mendoza