You nailed it
The aircraft will automatically descend and land if Failsafe RTH is triggered when the aircraft is with a 20 meter (65 feet) radius of the Home Point.
Found this on page 13 here:
https://dl.djicdn.com/downloads/phantom_3_standard/en/Phantom_3_Standard_User_Manual__V1.4.pdf
Not sure why they would design it that way though, if it has the capability to land much close to the home point. So if you want it to bring it self back to you then fly away further I guess, strange.
Thanks for the info though!