I think I've got it figured out. Pull the vapor into your mouth like a cigar. I'm not a big cigar guy but there is part of the concept that applies here IMO. You absorb nicotine from cigars through your mouth. Gradually, over time. If you took a hit on most cigars like you do a cigarette you'd get the same effect as you are vaping. If you don't cough immediately, it's gonna hurt. The trick is to pull the smoke/vapor into the mouth only. With a cigar this is a very manual process and the draw really depends on the types of tobacco, the wrap, the cut, and how far along you are. On the vaporizer it's the air holes, connection, tank - etc. But what you are doing is similar. Draw easy, steady hits into the mouth. (On a cigar you'd allow the majority of the smoke back out without inhaling.) Then you'd breathe in, with a small amount of smoke still in your mouth, adjusting the amount you inhale by the harshness of the cigar, or how close the ember is to your mouth. Similar idea to adding mixing air to the hit. You breathe the hit in with mixing air, not directly. This should ease the harshness and allow some of the vapor to cool that way.
Low quality juice that's high in pg and nic is going to hurt. It may make you cough. It makes me unhappy, light headed and sick feeling as well.
I have a 18mg menthol that's higher VG and I can take large draws on and breathe in almost directly without discomfort. The menthol adds a cool burn / numbing though so it may be suppressing cough. I tend to like cooler draws with it. It's a strong enough flavor that it doesn't need nuked or to taste hot. So I don't really run it over 9 watts.
It's my daily so far.
I have a blueberry vapor-x 18mg that makes me cough if I take anywhere near the same hits. It burns, (and makes me sick) and no amount of adjusting on the v/w makes a difference. Two big direct hits and I'd feel like something was standing on my chest. Cough 100% chance.
The fluid mix and technique matter IMO.
Not smoking AT ALL and just vaping allows you to retrain the technique IMO. But it's remotely similar to cigar smoking in concept.