You can manually spam clicks to target units farther from the orb. The gems fail to fair because just before they can “lock on” the target, the target usually reaches the orb first therefore the gem will try to find the next target and fail again because the next target reached the orb again.
You can circumvent this by spam clicking on a path that’s a little bit farther than your orb so that your gem will shoot creeps that are a bit farther away from the orb.
Or just place a blue/cyan gem near the orb.
This doesn’t happen with high level gems because they fire so fast the projectile reaches the target in no time. (and they die quickly too!) The speed of acquiring targets seems to be affected by firing speed too.