Both, for now you can work on the practice part.
For me, the biggest help was to break it down.
I could fly up, and slowly back down. Could I back down faster? Could I back down slowly with precision? That is reverse.
I could fly up diagonally, and back down diagonally. Could I back down at a different speed, or more precisely? Again, that is reverse.
I could do a dive stop and back up slightly to flip around. That little piece was reverse.
If you can hold an inverted hover, that is reversed against gravity. Hold it steady as long as you can. When you are ready, slowly back up more. As slowly as necessary, work to increase the height of the inverted hover. That's all reverse.
I could fly forward horizontal but reverse would flip, so I did it at an angle, about 30' or 60', backing up as triangles slowly. Go super slow at first.
Practice those elements. Look at ways you are already reversing and do more of it. Do it slowly with more deliberate motion. Hold on as long as you can. Try to recover when it flips, then try again to hold and repeat.
For tuning, as mentioned above, more brake helps. The default Rev leader lines have a lot of forward drive built in, but reverse is the opposite of forward drive. More brakes helps.