If I understand what you're saying, you're suggesting the 'extra payment' is if you're short of 11 months payments and you want the phone when it comes out. Yes, in that case you'd have to pay more to make yourself eligible for upgrade. But what I'm saying is, for people who will have paid 11 months in August, they could end up paying an EXTRA month while waiting around for the iPhone to be released. That's an extra payment because you only have to pay 11 months to upgrade, but if there's nothing to upgrade to then your existing contract is gonna keep charging you until you upgrade.
But what I've worked out, is that those of us not yet signed up, our payments will be taken towards the end of every month. Meaning if you get to August and you've paid your 11 months, you'll be eligible to upgrade when the iPhone 8 comes out early in September, before your September payment.
I hope that makes sense and that I've understood what you're saying.