For general safety reasons we tell the the aircraft to use its smart RTH function. This means the aircraft keeps track of how far it is from the home point and how far it can travel on the remaining battery. Once the home point is further away than it has power to return home it will head back. This can be avoided by using the Movable Home Point function which will update the home point as you fly which will affect this calculation and keep it in the air longer. You just have to stay pretty close to it.