He has done really well in the past in Masters events but not in the last year and a half.
In the last year for example he has won Miami but to be honest he didnt play that well and his main rivals all dropped out early.
Other than that he has reached one final but hasnt made a semi in any of the other Master events in the last year.
Given the amount of talent Murray has and how much better he is than the players outside the top four he should regularly be making semi finals.
I am not expecting him to be beating Djokavic, Nadal and Federer every week but he shouldnt need to to make semi finals most of the time.
To say he doesnt peak for Masters tournaments, I dont buy that, who does peak for them? Tennis players should all be geared up to performing at their peak in the Slams.