Well, I think it would help determine what your asking; i. e. What is a well trained small dog ?
I can answer about my Jack but is that the answer your looking for ? Is he small enough. No, he's not perfect in any way shape of form. But he is very trained in certain things. He loves to hunt for Gophers, loves digging at the campsite, (go to ground). He will jump on a 4' wall in less the two seconds when asked, if he wish's to do so. He will sit at every crosswalk on command and wait for the okay signal when the street is clear. He will jump up on the Park drinking fountain on command and stop like a cat to get a drink, although I don't allow that too often because it is not a safe practice, but he enjoys it. He will roll over and roll back upon command for a treat. He barks a lot. Very fast to see me grab my keys, a few doggie bags, put on my socks and shoes, he know's that outcome, but he's noisy. His manner's with other animals is fair at best. A very loving dog at 15" and 18.5 lbs. but he don't like chihuahua's.
Most small dogs are not controlled well because the owner thinks it's cute and sorry to say their wrong. Bad behavior needs constant - consistant attention. Nelson is wonderful with small children and they are told to hold their hand out and stand tall with their face out of reach. Children need to be instructed each and every time and the dog needs to hear the command gentle..
I would rate him a strong 5 on a 10 scale. He is not fearful of larger animals. Getting him to heel and keep his nose up is a constant. The leash goes forward and the head comes up, upon correction. Then after all the training is finished he get's playtime where were both in a more relaxed state. Nelson's Valor, JRT is Nov. 2006 (7). He loves his mommy, like chocolate cake.. No cake for the dog..
I hope at least I covered one of your questions..!!