I tried the RTH button and thought i could control height while it travels. But no. It would not respond to descend command. Is there a setting I'm missing?

Try again.  It works perfectly on mine.

Like Labroides said, try it again and let us know if it still persists.

Ok. Shall do.  

Todka Posted at 2016-12-24 11:30
Ok. Shall do.

Please keep us posted.

The only issue I have had with RTH is that no matter what height the drone is at, it goes UP another 98ft (if RTH was triggered at 200ft, it will rise to 298ft) which is really annoying..)  before returning home.. which can be good or can be bad depending on location..  other than that, it has worked ok for me..

I had RTH issue as well, although with the Mavic.  
1st there is 2 different docs for RTH.  The Mavic's Manual on pg 16 seems to be accurate, but this is NOT the info presented while flying, in a simulator, or in the DJI Beginner Tutorials. (Mostly around 5m - 20m from RTH varies).

Also, when my RTH issue occurred, it was flying at a tree, and my DOWN commands (or any for that matter) did not over-ride its route.  Hence, a broken drone now in the shop... :-(