The training of the plant can have something to do with it also open up the canopy make sure the bud site get plenty of light I’m not big on a whole lot of fan leaves and lose all the small popcorn bud down below they just take away from the big buds

also harvesting to soon can give you airy buds 

I’ve never have grown with HID I’ve always use LED where I can control the spectrum heavy blue in veg keeps nodes  closer not a lot of stretching then I push red spectrum for bloom increases yield and give her that last stretch Then Finnish with uv last two weeks 

It works for me 

also some sativa strains are known for being airy