The reason you can get more stoned off of less weed is becuase you're going after the thc. When you smoke more weed, you're getting more of the cbn cbcs rather than the thc, and the cbns and cbcs make the high different/weaker/take away from the thc high.
Thats why sometimes it's nice just to take one or two little puffs and see what happens, rather than go after a full bodyload and less of a high.