[wmf]

It may be possible to place caches deeper inside an ISP's network than the peering points. For example, it looks like Apple peers in Dallas but not Austin or Houston so putting a cache in Austin would save bandwidth up to Dallas.

[dfox]

In my experience it will invariably be placed deeper into the network, that is at least into network core of the ISP, which typically isn't anywhere near the edge router placed in some wonderfully expensive colo space associated with some IXP.