I know.  I’ve thought about this before too - and honestly, I think this is why it upsets me so much when people disregard Tyrion’s character.  You don’t see characters like Tyrion - positive representations of disability in the media are difficult to find, and Tyrion is a very visibly disabled character who shines in his own right.  He’s complex and multi-layered and neither entirely ‘good’ or ‘bad.’  He’s just very human - and any such character should be appreciated, but especially Tyrion who adds visbility to a cause that gets very little.

As for your question, the commonly accepted term is ‘little person,’ and that’s what I normally use, but of course the best course of action would be to allow the person in question to tell you how they choose to refer to themself.