Ah, yes, you are correct. An avatar "must be 110x170 pixels." I was confusing it with the wording for signatures, which "may not exceed" the stated size.The avatar needs to be 110x170 pixels. The 100 is width and 170 is height.
Hmmm... now that you mention it, I can also see a certain similarityVery pretty, Nyavene Sedai! It feels sort of related to your old one, so it won't be hard to make the mental switch.