Don't think you can change the size...but what I did was remove the "kill notices" in the options...so it doesn't give me a message each time someone dies. That way I can hear what the team is saying without having half my screen filled with text.
If I need to see how many ppl are still alive, I can see in the top left corner (with the new patch!)
If I need to see if I got a kill, I can check my k/d.
