Well, hopefully someone will stop by who's a bit more knowledgeable than me about WTS. I never used that technique, so can't speak to it.
As for WHY, my guess is overtired. You're getting about a 10 hour night's sleep, which at our house almost ALWAYS means overtired. When my son is teething, he gets extra tired and I've found I need to put him to bed a good 30 minutes earlier until he's over the worst of it.
I think I'd be inclined to try an earlier bedtime and see what happens. Could be your DS will just chat for that half hour, or he may fall asleep and get the extra rest he might be needing. That's my best guess! I know putting them to bed earlier when you're having EWs is scary, but it often works. Might be a simple thing to try.
Now, hopefully, someone will answer your questions about WTS!