question about Burning Strikes notable

If I'm correct, the attack has to inherently have physical damage in the hit for this to work, right? If a hit is converted to %100 fire damage as in armour explosion, it is not getting an additional %12 on top of that right? Nor is it getting it on the front end from flat physical attack that armour explosion is converting, correct?

So if I'm procing armour explosion from stampede, the only difference this notable would make is in the damage of stampede itself, but does not continue down the chain at any point. Am I understanding this correctly?

Also, if I take avatar of fire, armour explosion will still check for my flat physical damage with no penalty (25% less damage) that the rest of my attacks will suffer, right?