Thanks for the update and pics!

As far as I can tell from the pics, the top is pulling in and, therefore, external support won't do any good

It's your pool and you can do whatever you want with it but, my considered opinion is that adding more bracing will simply be a 'waste' of time and energy (take a look at my previous post for the real cause of this).

I don't see this as a serious probem, but check the things I mentioned when you next install a new liner.