I think there is a bit of circular reasoning here. If by "physics" we mean the way the universe works, then of course we are "within physics", and we determine our actions in exactly the same way as the rock falls to the ground : because this is the laws of physics that those things happen. The actual distinction is what people attribute to the term "physics" itself. For some it is exhaustive and it encompasses everything that exists, but for others it is not and they allow "something else" to intervene. At which point we're well within the realm of theological arguments.