Hi Mike,
In my oppinion the overall pie recipe should be adjusted not just to suite individual carpets but for diferent segments of any given carpet.
If, in the interest of brevity, we disregard the innitial preparation, (inspect, prevac, spot etc.) and concider just HWE we then make certain choices:
Pre-spray. Generally an enzyme pre-spay will require more dwell time and less agitation than most TLC's or One-step. (optimum heat of pre-spray varies also)
Extraction. The choice of extraction additive will determine the amount of heat - e.g. applying Liquid Woolsafe at >60c defeats the object of useing that product.
I could go on, but will mearly say that the pie composition is infinitely variable and that as an experienced cook may not weigh all ingredients, so experienced carpet cleaners will adjust 'on the fly'.
John.