That peak is a characteristic of the RS meter, and is much worse in the newer meters than it was in the older ones. There used to be a graph of the response in the manual for the meter, but it doesn't appear in the latest ones (wonder why
) but while searching for it I did come across this article which looks in detail at the response of the RS meter:
http://www.audioxpress.com/magsdirx/...a/koya2811.pdf