BAT should ideally look and feel like the dog is off leash, except that you are keeping things at enough of a distance that your dog can't accidentally go so close that he gets scared. The dog is the gas and you are the brakes.
Generally speaking, we avoid walking the dog toward the trigger. Our movements should be in a neutral direction or away from the trigger. You might very occasionally ask your dog, "hey, do you want to go this way?" with your body language, but pay close attention to the answer. If your dog is hesitant or doesn't want to go, that's absolutely his choice.
Film your session so you can watch to see if there are ways to help your dog feel more free during the training.
The level of stress should be kind of like a puppy play time with two dogs that enjoy each other's company. In a play time, sometimes one accidentally gets too close, but the other can give a cut-off signal and move away, or the other guy does.
Dogs learn this communication naturally through negative reinforcement (the dog giving the cut off signal gets a break) and positive reinforcement (the dog allowing the other dog to have a break gets rewarded by resuming the interaction) in puppy classes and play times. Puppy play times need to be set up to be safe, so they can learn to be more and more confident.
But even with that, puppies are learning through negative reinforcement in your puppy class. Don't worry. That's naturally occurring reinforcement, not kind of negative reinforcement that we definitely want to avoid, like leaning toward the dog to get a sit or pinching their ears to get them to take hold of a fetch dummy. You aren't adding any aversive stimuli beyond what's already out there, and you've set it up to be as safe as possible - it's a natural learning process about how the world works.
When working with fear or aggression, BAT is very similar to the early socialization for puppies. In both, we use some treats when necessary, but not too many, because the dog can learn more from the situation itself than from us. One major difference is that when we are doing BAT with a dog who is afraid, we can't allow the dog to run up and get into trouble, so we slow them down at a distance to let them engage with the trigger from a (mentally & physically) safe spot.
BAT gives the animal a chance to learn and practice communication. This allows them to desensitize to the trigger and also change their emotional response.
Over time, they gradually get closer and closer to other dogs, people, etc. and start to get positive reinforcement from the social interaction. That's why it's important to do multiple sessions with the same decoy, if you can, so the dogs can end up engaging in a friendly social way (which may just be exploring the same smells together, not wrestling, etc.). That's true for issues with people as well.
If this isn't what your sessions feel like, focus on learning how to handle a long line. Click here for a PDf with some tips.