I think it's pretty clear that having full back tension is more important than where your anchor is. That said, it's also essential to have a consistent anchor so that your sight picture stays consistent.
Part of the issue is, IMO, that we tend to think of the anchor as anchoring something, which it really doesn't. It's more analogous to the way you lay your cheek against a rifle stock - it puts you in the same relationship to your sights each time, but the archer's "anchor" doesn't really anchor anything, the back tension does that. As long as the way your string hand touches your face is consistent, you're getting what you need out of the "anchor."
Take a look at Robtatto's post under "Anchor v. Reference" in this forum for a thorough explanation.