Sheep are funny critters because they don't always do anything the same. Remember great eyes and noses and they use both well. When I try to spot them it could be from above or level or below. Once you have spotted them coming up at them is a very hard thing to do, thermals. Coming in from level or above are the best ways. But anyway you do it, you pay serious attention to what they are doing. Here in CO they move up and down the mountain sides and do use timber. I will say that once they are above timberline they are easier to spot but they spot you much easier also.
When I killed my ram in 2000, he was part of a group of 5. They were coming out of timber at timberline over a half mile away across the basin at 5pm. I shot my ram at 7:50pm almost a mile from where I spotted them. They were slowly gaining elevation heading across the basin. It was a very hard stalk because there was little to no cover for the stalk. When they crossed a small ridge I was able to gain the ground needed for a 55yd shot with my bow.
Sheep are amazing animals but they will test you.