I am fairly new to FPV, Some of you here helped me build my long range quad. And she is a beauty

Now I am going out testing her in the swiss alps. Now I have some questions;

1. where is an idea position for me when I want to attempt a mountain dive ? Is it better for me to be at the bottom or is it better to be up top and dive down. 

2. I am picking up some 3700 mah 4s lipos,  will that get me enough power to fly up a 500 - 800 meters mountain and dive down ? 

looking forward to your feed back.

I don't think it will be any difference if you are flying the same path because exchaging places just put the tx/rx on the same spots, just reversed. What you want is to have the most air gap between ground and tx/rx due to signal reflections so for example you can try to stay yourself high but not in the same ground plane of the dive. If it was a valley I would stay at the same level high or at the middle of the opposite side of the valey as long as you have video and rf power to transmit. Just a personal opinion, I never did any a montain dive, just take it with a grain of salt

To get that cinematic effect that you see on youtube videos you are going to want to dive down. What I like to do is surf the mountain peaks and pick a spot and just go for it. 
Here is a video from RCSchim. I have seen him on this forum and watch his videos regularly. He does some really awesome dives in the alps.  Gives you a good perspective on how to perform a good mountain dive.

It can matter.  But most of the time it won't matter.   Reconning your flight area ahead of time is important to avoid crashes or loss of the quad.  

You can always fly the route a few times before going for the awesome cut.  The real good guys do that, so they know the flight very well so not make a mistake during the flight you finally see on YT.

Thank you everyone for he helpful tips.