PoE cptcornflakes builds

Hi, I've been looking at some pyroclast miners over on poeninja and I noticed 2 lvl 100 ones were running High-Impact mine support on top of their pyroclast mine. I'm assuming it's because pyroclast mine has a duration and thus allows you to easily get to the 100% chance to deal double damage, thus making it a great support gem? Does anyone know if that's how that interaction works? Another thing I noticed whilst looking at both characters was that on top of running High-Impact mine (I'm assuming) for the double damage, they're running Annihilating light, but doesn't that cancel out the doubl