In digging in deeper to patients responsiveness to treatment and physiological profiles, it is starting to get less intuitive.  For example, this study shows that baseline increase in heart rate in patients with claustrophobia correlates with likelihood to respond to treatment.  So there seems to be a phenomenon of blunting of the HPAA in some conditions, (obesity, depression) which is not healthy. Chronic stress blunts the cortisol response, leading to burn out etc…
J Anxiety Disord. 2008 Oct;22(7):1101-9. doi: 10.1016/j.janxdis.2007.11.009. Epub 2007 Nov 21.
And yet they correlate: psychophysiological activation predicts self-report outcomes of exposure therapy in claustrophobia.

Abstract

The study examines whether self-reported fear and physiological activation are concordant when claustrophobic patients are exposed to small spaces, whether the measures change in synchrony for individual patients and whether initial activation of measures can predict the outcome of an exposure treatment. Ten patients with claustrophobia participated in six in-vivo exposure sessions with continuous monitoring of self-reported fear and their EKG. Partial pressure of carbon dioxide (pCO(2)), a measure of hyperventilation, was available in a subsample of patients. While evidence for concordance of self-reported fear and heart rate was limited, the measures changed synchronously within subjects. Most importantly, higher heart rate at the beginning of the first exposure session predicted better treatment outcome. Because self-reported fear turned out not to be a reliable predictor of the outcome, this is interpreted as evidence for the incremental validity of physiological measures of fear.