v1.5.7b IH 5.1.9 Zen Colorbox Responsive Classic template site

is this normal behaviour? if not then have I missed a configuration somewhere? - clicking on additional images opens the image in a lightbox but the lightbox and hence the image is even smaller than the additional image size, with left right arrows inside the box? hovering over the additional images shows a larger size image in a popup hover box which is great, but clicking on the image isnt.

All images on the product page have the clickable text 'larger image' so it creates some confusion.

cheers, Mike