I had to experiment a fair bit to get my technique rolling and even now I often don't break through but that's mainly due to not taking the follow up hit. I found using brillo for my screen helped ensure the spice didn't melt through. I couldn't find a GVG and haven't ordered one but I really like my clear glass Sherlock pipe, I can see the vapour and it helps me time my inhale. Other than that it's just a matter of inhaling as long as you can and holding that spice vap in until I think I could black out. Usually I don't exhale until the CEV geometrics go BLAM. There's plenty of times I've just thrown technique out the window bogged down on the pipe balls to the wall hard and held er in like I was chained to the bottom of the ocean and have had awesome sub breakthrough experiences.
I would suggest mastering the single blast as it seems your not giving the DMT enough time to absorb and hit the old noodle. trust me you can go farther than you have with a good single hit, all but 1 of my breakthroughs have been off 1 hit. By the way I probably tried it over 20 times before I broke through and no one I know personally seems to be able to smoke it correctly.