Even if you pack it quite loose, the air gap between the cap and the tip is quite restrictive when you close the air hole (carb). I've heard people suck it really hard, but in my experience, you don't need to. Sucking hard has no noticeable effect or more airflow. A slight sucking pressure is all that's needed to have the air flow through, heat up and create vapour.
You can partially open the carb, or "feather" it to cool down further - I usually don't open until the end, or as soon as I feel my throat tickle. When you open the carb, it clears the condensor tube of vapour, but vapour through the tip is greatly reduced.
As for MTL/DTL, whatever suites your style - I find MTL easier with the restricted airflow, but you can definitely do DTL with the carb more open I guess.
One thing that helped me, was to attach clear tubing to the mouth piece (some suitable sized clear silicone tubing works fine) so I can see the smoke coming through. You can then easily see the effect of the pull and get an idea of when there is no more vapour to inhale.
One session of 4-5 drags with ~0.1g herb is usually enough for me. With quality bud you should not have to struggle unless your tolerance is very high.
Oh, and also check the tightness of the cap on the tip - sometimes it deforms a little which might also affect airflow. There are some good vids that show you how to do this.