Blindfold Shuffleboard, i fail to understand the logic or is it a bug?

Hello,
I'm hooked to the blindfold games like so many others. My latest addiction is the Shuffleboard game, however there's one thing i don't get the hang of and it's the "flicking" bit. To me a flick is a rapid movement with the fingers as oposed to dragging or swiping which is a slower movement, at least in my vocabulary. Here's the problem though: I'm in the practice section of the shuffleboard game and am trying to flick the discs so that they get in the scoring zone. Sometimes i swipe slowly and the game says that my flick lasted for something like 0.3 seconds and of course the disc goes way to far, so i try flicking slower keeping my finger longer on the screen and the same thing happens. Then at other times i flick quite fast and i get a perfect 10 point hit but when trying to flick at the same speed and so on, the game thinks i'm flicking slower or faster and it all seems to be random. I just fail to understand the logic of this.
I'm using an iPhone 6S+. What am i doing wrong?