When he first joined I'd argue there was a few goals we conceded where he should have done better, I recall him being beaten at his near post early on. Since then to be fair as you say he's not really had much to do and certainly no goal is directly his fault.
There's not really enough of a sample size to make a decision. The ball just doesn't come at him often enough. One thing I'll say is that none of the goals against were as a result of errors from him so cant ask for much more than that.