I think rather than comparing ratings for the episode number, we could perhaps look at the equivalent episode from around this time last year which was Amy's Choice, which got 6.2 in the overnights. In comparison we are looking at only a 300k difference between the equivalent episode last year. The ratings are pretty stable this year, with quite large time shift figures. This series has started later and rather than viewer fatigue, to me, it is just a case of people are able to be out doing more things in the middle of may rather than earlier in the previous year when the numbered episode aired.