To be fair, I think @texphoto is pointing out that in a zoom lens such as a 70-200mm the lens hood limits the angle of incident light to the front element the same regardless of the internal positions of the zoom mechanism. This much is true. However, he's not correct in his statement (I'm paraphrasing) that the zoom position doesn't matter at all. Clearly, at 200mm the front element is being exposed to a far greater angle of incident light than will be in the field of view of the lens which is how flare is created
You guys are missing the point entirely. If you are shooting a 70-200 zoom, and you have the stock hood: you have 2 choices: Use the hood or don't. Which of these 2 choices will better control flair at 70mm? Using the Hood. Which will control flair better at 200mm? Using the hood. In fact, if the hood is preventing all flair at 70mm, I will guarantee there is no flair when zoomed to 200mm assuming no other changes.
Now if you want to argue that you should not use the hood you have because a theoretical 200mm only hood (that you do not have) would be better than the stock hood, then you are right from a theoretical standpoint, but wrong from a reducing flair/practical/not just being difficult standpoint. Now if anyone here owns a 200mm only hood for their 70-200, I will... eat a bug/admit defeat/ etc Whatever.