I don't notice the cones unless I turn the light higher than 12 inside or in a darker room. And in a darker room I would not really go above 10, so I don't see it. I know its there as I turned the light all the way up to see when I first got it. But since I never see it, I don't care.
Its like I know I have dustbunnies behind the sofa and probably some other items, but I don't see them.
Lately I have been happy with light at 9-10 at all times. Seems to work for me. I have bad eyes and I am night blind-ish. But if I can see the screen "glow", I know I have the light on too high. Outside it doesn't really matter at all for me as it looks the same if I have it on 0 or on 20. Can't tell a difference. But I read mostly inside so I like a little brighter backround. But not lit, if that makes sense.