Unfortunately peppers do run wild in heat range, found this out first hand at a mexican place I like, sometimes the sauce is hot sometimes it aint. So I asked what they did different and was told that they use the same recipie everytime but the peppers vary in heat. I've also heard that smoked Jalapeno's will get hotter when smoked ( Chipolte ), due to the decrease of water content and the oils being brought out during cooking.
Me I'm gonna try habs stuffed with cheese and bacon come this summer when the plants start putting off some fruit!!