For flavor, growing conditions can make a huge difference. My wife can tell the difference between a tomato grown in the soil and in a container. I cant, but I have tested her and she didnt make it up. Same variety too. I gotta figure heat is effected in the same way, but I dont know what lends itself to making more heat.
I think it was Nigel from Hippie Seed who said that run off from their worm farm helps up the SHU. Now canabis growers swear that resin production is encouraged by torturing the poor plant, starving it of water, shoving tooth picks in the stem, ,and so on. But I do not know that pepper plants respond in the same way. I also think some of the canabis growers are as nutty as I am. I swear by aged duck poop.
Heck, if it was Nigel (bad memory here) and we ever talk I am going to propose a fun / silly competition: Worm Juice vs. Duck Poop. Kind of want to return some of the fun to the whole which is hottest thing. So much mean spirit now that there is money in who ever is the hottest.