Why not set the max decent rate at 6 m/s above about 100 feet altitude so that I can recover my Phantom from altitude before it runs out of power?

The decent rate is set at 2 m/s, and 0,6 m/s during failsafe. Your requested 6 m/s would cause an almost instant VRS issue and your phantom would crash to earth at 9.81 m/s

I think you need to read up on vortex ring state aka propwash or wobble of death. The props will lose lift and your phantom would be uncontrollable.

By the way, if you're hoping for more responses, post under "hantom" topic as this "Report an issue" is meant for issues concerning this forum, not your quad.