I have had does and younger bucks come to a bleat call. I have also grunted bucks to my stand, sometimes from across a large field.

Do you control your scent well? This could be an issue.

Maybe you are just too fare off of their normal path and you should move your stand. Do you always see them in the same area? Do you see them regularly? Do they seem to get alarmed when they are getting close to your shooting range? Do you have good camo for your surroundings that does not make you appear like a large dark blob on the side of a tree?

Sorry to ask so many questions, just trying to eliminate possible reasons for the distance.