This is something that is brought up a lot. Here is my advice.
If your raid leader says to do something, you should probably do it, even if it is less than optimal for you. It's not all about you, it's about killing the boss.
However, if he comes to you afterwards and complains about your dps, that's when you need to explain to him why your dps is doing so poorly, and changing the strat a bit can improve dps by a lot, not just for you, but for the other casters as well.
Or you can be proactive about it and discuss it with him beforehand, and again, explain that if he wants some decent dps from you, he's going to have to be a little more flexible about positioning.
Either way, try to discuss these things outside of raid time
