This is similar to much of my flying, in the scottish mountains looking at deer herd movements. I take off from a lodge, fly up to the hill top, where the deer often are, in a dip by a pond, and if i dont find them i go over the top to look for them. However, i dont dip down on the far side, as you just lose signal. I can dip a little, but generally its just seconds below the skyline and if you are there for any length of time you just lose signal, so stay high above the tops and its fine. As soon as signal wobbles i push up on the left stick and in most cases it will be rising as soon as the signal is strong again. You will be able to look over just as well from a height above the hill top
I fly in a few similar situations, and generally plan to reset RTH when i get to the maximum planned height if the area is complex and new, and this has helped a few times. Just remember, when returning to home after flying up a mountain, that you could be very high up above the launch site, but its great fun to be whizzing down the valley at speed on the way home. I also find that returning home, flying forward and down uses way more battery than i would have expected, its not like returning at a constant altitude, so this needs to be considered. It may be just me and my drones, but its worth considering and watching for.