For that smooth hit you're referring to as Katya is pointing out, you have to remember your e-liquid is being vaporized off of a carrier material which is the silicia wick, it will only burn as much liquid as it holds and once it's done burning through that liquid you'll start getting that uncomfortable, scratchy hit that you're referring to, which is a dry hit. To rectify this, you have to remember that you're heating element is sitting at the top of your tank, even though the wicks are going downwards it doesn't always mean juice flows to the top as smooth as it should be or as fast. What you'd want to do is tilt it at a 45 degree angle when you're vaping all the way up to a 90 degree angle (sometimes more), as the level of the liquid decreases. What you're aiming to achieve is to get the liquid soaked into the wicks as smoothly and as quickly replacing whatever's been vaporized off quickly.