I’ll preface this saying I don’t have much experience at all painting. Having said that I think the ear looks flat because there’s not much contrast in value in and around it.
Some areas around the ear should be darker because they are in shadow, specifically thinking of the neck area.
I think adding wider variation in value to the hair on the ear could also help.
A lot of the volume comes from context so when you do a bit more on the neck and what’s around it the ear will look very different!