One of the nasty things Hirano Aya is called by her 2channel detractors is "Deko Bitch," "deko" meaning "forehead."
She certainly does have a high forehead, which is one reason she has usually worn a hairstyle with her hair covering at least part of her forehead.
But one of the things I like about her is that she seems able to poke fun at herself. She did that in her blog today. She posted a photo of a birthday dinner at a restaurant with her core support staff. (click photos to enlarge)
The photo is dark, so you can see almost no-one clearly except her. She writes: "It's really dark. I'm the only one that's bright. Why is that? Reflection off my forehead?"
By the way, check this post on j1m0ne's blog for a reference to Aya in episode one of Kannagi.