slapo
It's... alive!
I think it actually looks like some areas are practically overshaved (jaw line, cheeks closer to the mouth), and some, as you've observed, a little undershaved (neck and a part of the chin).From the pictures appear that you still have plenty of growth to perform an ATG up-down pass. My suggestion is to get a razor that’s more efficient, to cut more hair on the first pass, if you want to maintain your WTG-ATG routine, or don’t go ATG on your problem spots.
I wonder whether going XTG on the first pass wouldn't help - it should cause resistance from hair (so no irritation either), but might yield a slightly closer shave.