As a rule, you cannot brake at the same point you normally do, while following someone. 95% of the time, you will have to brake earlier. Even if they brake as late as you, you will hit them if you don't brake earlier. If they brake sooner, you will really have a problem. The only time I have ever been able to use my same braking points, is when I am following a well tuned, well driven Elise. They can go deeper then I can in the Vette, thus no issue.
This is what causes a ton of the punts I see. People just don't realise they can't drive their "normal" line. You must adjust for those in front of you. Basically, the only time you should be braking late while someone is in front of you, is when you are along side of them, out braking them for the pass.