18" is the typical distance I would keep my HPS bulb from the top of the canopy. going closer encourages stress and the bleaching effect can be seen on your plants if too close.
what kind of reflector are you using?
what are the temperatures in your room like?
also.. some strains will just be denser than others. the ones you have listed are not what I would consider to be quality genetics... although I am a little picky when it comes to genetics and strain choices and I stay the hell away from autos and fem seeds.
pick up a pack of Bodhi gear. get something that will make a decent yielding crop with big dense nugs..like his tigersmilk any of those 88g13hp crosses.
do your best to keep the top of the canopy even.. and blow a fan over the top of the canopy..not directly on the plants. raise and lower your light as needed. keep temps as close to 70F as possible and humidity low but not too low.
it takes some trial and error but with each grow we learn what's best for us and the plant. you'll get there.
environment makes for 90% what you need to pull off a successful grow.. good genetics, patience, and a proper nutrient regiment make up for the rest.
good luck!