thanks Reely340 for so clearly stating the question!
What I am stating is that in c below, the application of original power of 80% will not steady the descent, because in a slight descent of say 250 fpm, the power needed is more than 80%, it might be 85%. So if you restore the power while descending at 250 fpm to 80%, the aircraft continues to have a power deficit and will increase its descent rate. To arrest a descent of 250fpm , you must pull 85% torque. (all these numbers are hypothetical, but illustrate the issue.
If I could draw a power required curve for you, it would look like the line for -500 foot rate of descent crossed over the level flight one, so a steady descent of 500 fpm takes much more power than steady OGE hover.