Is this normal on 100% photochromic lenses?

Hi,

I just got these 100% photochromic sunglasses and noticed something weird with the tint.

At the bottom of the lens, the photochromic tint seems to stop very sharply. You can clearly see a line where the lens suddenly becomes lighter (circled in the photo).

Is this normal for 100% photochromic lenses, or does it look like a defect?

Thanks!