I see MCE as a standard which all students are measured by. If one's English is at the MCE level, he has satisfied the requirement. Right? So "at" that level, it becomes the passing point. Below that, one will be considered failing. If you ask me, what is the most common prep. to go with "level", I won't hesitate to say "at". The original sentence wasn't very natural with the way it was constructed. That's why I revised it. I guess one may guess that meaning but to be grammatically sound, I personally won't use "for" with that sentence. I guess that's the best I can explain it. Again, it has a lot to do with the contexts.