The 1/3 mark is a good general rule, but the terrain features will dictate exactly where they will bed. I start high and look for benches, shelves, knolls and old logging roads. This is where deer will bed.
The thermal tunnel is only part of the equation. Mountain deer also rely heavily on their eyesight when bedding. The features above give deer the best vantage point and also gives them the path of least resistance.
You need to be hunting where the sign is, but it gets tricky in a hurry the farther down the mountain you go due to the wind/thermal. You need to find a spot where the leeward wind makes the deer comfortable, but also blows your scent off the mountain. This means you need to hunt above the thermal tunnel or on the side of the mountain.
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