I have not personally tried using a white rag so no experience here but I was once trying to sneak in on a herd of a few does and a buck. As I was walking I looked and they had me pegged at about 400 yards. Because of the terrain I believe the could only see me from my chest up. Once I realized I was seen I ducked down. Next thing I know the buck is running to me stopping occasionally to try and see me. He closed the distance so quick I had to hurry to get my bi-pods set up and get ready for the shot. Shot him around 100-150 yards. I was in camo. I believe if I had a decoy he would have come in for a bow shot.
Having said all of that. I really believe how much pressure is on the antelope your are hunting. I could be wrong but I believe that unpressured antelope are more likely to fall for our "tricks" compared to pressured goats.