I was thinking Clark was too close to it to have his powers, and Kara was far enough away to still be fully functional
That may be so, but even so it opens the door for clark to shoot the Green K from a distance in any situation. Also, I thought green K turned black when heated?

I'd love to hear about it and what Clark's parents really wanted from him
Me too. I'm still very frustrated by the way Clark NEVER asks questions of the people who could tell him the truth about his heritage--Jor-El, now Kara... and apparently Kara's also easily distracted from that important role that she could play.