If a dog indicates when he’s within the scent cone, without following it back to source, that’s an undesirable “fringe” response that may reflect a deficit in training where the team can improve. If your dog exhibits a fringe response during UKC Nosework competition, you may still pass/qualify, but that behavior will be faulted.
It’s important to be clear in training that being in the scent cone isn’t rewarded, but rather, rewards only happen exactly AT source (or approx. within 2-6 inches).
Be careful to reward the dog for being at source, and to place the rewards at source. Don’t reward the dog for being “close”, or that behaviour will happen more often. Don’t deliver rewards away from source, because you’re losing an opportunity to build value for the dog while he’s at source, sniffing the target odor. By providing clear, precise rewards over many searches, the dog’s sourcing will improve quickly. (The more unclear you are, the more confusing it will be, and learning will take significantly longer.)