I don't understand it either, why some have a gentle 'build', and still others start and end hot.
I don't think that the scoville unit applies to that kind of heat, but I know what you mean.
I know that the degree of hotness depends on the cultivar, genetic breeding, available nutrients, available water and sunlight while growing, etc.
A fully mature hot pepper will start 'corking' ( a brown patch forming on the exterior skin), so it tells you when it is ripe.
The novice gardener generally believes that this 'corking' occurs as a form of sunburn, whereas it actually is the plant stating that it is fully ripe.
Yes, I have had oriental hot peppers that have a 'build', whereas ,to me, Spanish and South American peppers seem hot from beginning to end. I don't know why .
My favorite cooking pepper is the African birds eye pepper.
Starts hot but ends with just a tingle. Great on chicken. I mean REALLY great.
Add some garlic and you have Nandos. http://www.nandos.com/
Scrumptious. They have built an empire on it.
And thanks for the corking thing. Gave me insight into which seeds to save.