Ive smoke H quite a bit, usually the high is pretty good, and for me, it lasts pretty long too, I usually put about a match head size of dope on foil and put straw in my mouth, fire it up and suck in all the smoke, it is pretty strong, so you wont need much smoke everytime you hit it, you should be able to hit each point, about 3-4 times, then it will be burnt up for the most part, leaving a crusty black material, that is basically just black ash.
However it seems to be stronger right before it wont produce smoke anymore and it totally burnt up, Im not sure if the materials its cut with burn up first, or the dope burns up first...anyone know? If I had to guess id say the impurities burn up first