From Hangar's flightschool:
Start Condition Applies when Lost Connection is End Mission
None Autopilot will fly to the Mission Start location from any distance.
Start Point Proximity Autopilot will only fly to the Mission Start location from a specified distance.
Distance (Start Point Proximity) Applies when Start Condition is Start Point Proximity
The maximum lateral distance from the Mission Start location that Autopilot is allowed to control the aircraft movement (effectively a cylinder of infinite altitude). If the aircraft is outside of this cylinder, the operator must manually fly the aircraft closer to the Mission Start location before Autopilot will take control. Autopilot will immediately take control of the aircraft once it enters the cylinder. The Mission Start location is defined by the Mission Start marker, or a designated Checkpoint, or the first Waypoint, in that order.