Question about flying over abrupt drop offs and how the Phantom 3 handles the sudden change in altitude

So I'm planning on taking my P3 Pro up to my fiance's cabin in the Blueridge Mountains this weekend to do some flying. The cabin is on the very top of a mountain that overlooks a valley and as a result there is about a 1000 foot drop off into a valley at the edge of the driveway where the P3 will be launching from. This means that once I fly the P3 out over the edge of the driveway it's suddenly going to go from being about 30ft above ground level to about 1030ft above ground level and having never flown it in a situation like this before I have some questions about how it's going to react to a few things:

1. The max altitude setting on my P3 is currently set to around 400 feet. When the P3 suddenly finds itself over 1000ft above ground level how is it going to react to this? Is it going to try to automatically descend to the max altitude resulting in it descending about 600 feet down into the valley? Is it going to prevent me from ascending any higher, even though I'll only be about 30ft above the level of the driveway and nowhere near even the height of the trees surrounding the house? Should I just turn off the altitude limit altogether in this scenario?

2. I have the failsafe height on RTH set to 100 feet. If I were to fly it out into the valley and descend, say 100 feet, I'm now roughly 100 feet below the driveway level but still about 900 feet above the floor of the valley. If I were to lose signal and the P3 initiates a RTH, is it going to think "hey I'm at 900 feet, no need to ascend any higher before returning to home and then head back towards the driveway at its current height resulting in it running into the side of the mountain?