Thanks for the input. I Just kept thinking I needed to jump a little.
Generally jumps are designed that if you carry enough speed into them, you should clear them doing a straight air. Now the jump at your park could be constructed poorly, but that's unlikely unless everyone else is also knuckling. More than likely you need to carry more speed, also make sure you aren't "absorbing" the jump into your legs.
What I mean by this is that you need to bend your knees before the jump starts getting steep, if you bend your knees or lift your legs up as you're going off the lip, the lip of the jump won't launch you into the air as it's supposed to do, and you'll probably be hitting the knuckle. It might be that you're trying to jump too early, and this is causing you not to get launched into the air as you're supposed to.
Now spinning is a different story, but if you're just learning to straight air off park kickers, let the kicker do the work for you!