Just guessing here, but I suspect the flavor enhancer is
vape Wizard type enhancer, which blends the flavors and increases fullness of flavor and vapor. As for the strength, they suggest using 10-15% for the flavors they sell, so I would guess the regular flavors are around 10% and the double is closer to 15%... All of this is a wild guess of course, why don't you write Jason and ask, he was very responsive to my emails. Very good
juice and the price is right up my alley both for finished and DIY.