Do a controlled test.
With NAZA on, take off and try and acquire 9/10 sats in the air.
Set a new home pos by flicking the left toggle (S2) until you see rapid green flashing lights. Read below on proper HOME POS and COURSE LOCK.
Mark your new home point right below it.
fly to new locations and activate the failsafe.
Another thing is to watch your GPS as it descends automatically. If you are in confined spaces, chances your gps may drop to less than 6 and ATTI landing occurs where it may drift based on wind conditions.
I cant find the link right now, but you can always do the drone expert GPS Foil mod to increase GPS accuracy.
Home and Course Lock
***LEFT TOGGLE SWITCH***
1 = IOC Off
2 = CL
3 = HL
New Course Lock. this will lock the direction based on the phantom is facing. Flick between position 1 and 2 x 5.
New Home Lock. this will lock the new home position. Flick between position 2 and 3 x 5.
Wait for rapid green flashes for both the above.