Thing
I go with Genghis on that. I am sure you have tried an exercise at altitude of flying an airspeed in the descent?
You cruise at 100 kts and push the nose over! To maintain that 100 kts you have to bring back power. Note descent rate.
Now push the nose over even further! again to maintain your 100 kts you will have to bring back power even further. Note descent rate now!!
Push the nose even further and you maybe back on the stops with power you can no longer maintain 100 kts clean without chucking out some drag as now the energy you are getting from the airframe exceeds the amount required to maintain the 100 kts.
You can no longer play the two energy sources as your powerplant is at idle and you cannot reduce that further.
To maintain the 100 kts all you can do is to reduce the power from the second energy source by reducing the descent.
Of course you could hang out drag but thats another subject.
Pace