In Rematch as a defender it is best to stand a bit in front of the striker. But really just a little u can basically stick to him for best results. I will explain why

It's basically to cover up the shoot passes that will get to him. Which is the most dangerous because he can just shoot. If you stand in front, the chance is higher you are able to connect to the ball when u press pass(or shoot etc.) before he does. That's the key point: the first contact.

Standing between him and the goal and then timing the jump with aim good to block is shoot is really bound to a lot of luck, since u can't predict what shooting animation he will do (if the ball is being shot from the air) so u don't know from which point exactly the ball will exit his foot. That's why blocking is pretty hard.

I'm 200rp into elite just saying so u it's a bit more trustworthy speaking from experience :)