It's hard to gauge from the word "harshness" the exact sensation you're referring to. My experience isn't too much greater than yours, but I've discovered there are two very different sensations at the back of my throat from a good hit or a bad one. "Good throat hit" should feel warm, solid but not uncomfortable -- very, very close to the same sensation you would get from taking a good, long pull on an analog cigarette.
"Bad throat hit", though, is a burning sensation at the back of the throat that can trigger a "scratchy" feeling that makes you want to cough. At some point, you'll probably have experienced both and will even be able to tell that your cartomizer or cartridge needs a refill based on feeling the throat hit start to go from the former to the latter.
Also, I agree with onfire -- check your cart/carto/
tank to make sure you aren't low on
juice, try a
juice with a lower nicotine strength, and in the event you're using a variable-voltage e-cig, try adjusting the voltage downward until you get that "good throat hit."