Anyone have a small dog that's afraid of other small dogs but loves big ones?

my six pound papillon loves dogs much bigger than her. My sister has a corgi and corgi/american eskimo and she loves to chase them and smell them and get them to play with her. Even my sister's neighbor's giant black lab she loves to sniff and he cries when she's around. haha but when she's with little dogs, like my friend's boston terrier and pug, and they try to sniff her, she quickly sits down and starts to almost shake. I think it's so funny. Anyone else's dog do this?