On the Naza V2/Lite IIRC you couldn't change RTH height in assistant, however you can set home point 'in the air' to increase RTH height.
Say your flying near tree's which are say 30M high, if you hover 15M over safe landing point and set home position (toggle IOC switch 6 times I think?) and watch for flashing LED, then if you RTH it will go 20M above that height (ie 35M altitude), fly back to home point then gently descend until it touches the ground before switching off - I tested this with Phantom v1.1.1 ages ago as I was flying over a cliff from the beach and it works fine.
Low battery I think is land only with the Naza V2/Lite, you can set the warning voltage but it only flashes the LED which isn't brilliantly visible, best is to set a timer to half your flight time and use that as a signal to come back and be ready to land so you don't push your luck.