Sorry if this has been addressed. My house is surrounded by trees and I usually need to fly up about 60 feet to clear it and then go forward.

If RTH is needed does it know to do the opposite when coming home where it will adjust it's height etc? Hope this makes sense.

Yes it does, AC will rise to the height you set, it will fly at that height until it is directly over the home point and then will descend directly to the home point.

I'm not sure what you mean about knowing to do the opposite thing...  When RTH is initiated it will return home at the height you've set for the RTH altitude, or at the Mavic's current height if it's already higher than the set RTH altitude. The manual also lists a couple of exceptions to this rule if RTH is initiated within 5m or 20m from the Home Point.