Umm if you smoke cigs you'd know it doesn't matter what finger you rest the cig on, its still gunna stink up your entire hand and pretty much everything else in the immediate area. There's a pretty simple answer to the ops question. The next time you smoke a joint and you get down to the ass end. Tell me which is easier, hitting it between your index and middle fingers. Or your index and thumb. when the j gets down to the ass end, your thumb works as a nice platform to keep the j in control. If you where to do the same thing with your index and mid finger, you have much less control. Seriously try it when you only have a couple inches left and you'll know what im talking about.