When you are viewing the reviews, there is an option to filter displayed reviews to only the currently displayed "style" or subitem. Go down to the reviews and select "See all reviews" and a list of filter selectors will become visible at the top of the displayed results. Where it says "All formats" you can drop down and change this to "Show only reviews for <variation-type>: <variant> [| ...]" where the variant info is based on whatever product you were actually looking for.
Too bad this isn't the default. Or better yet, something like "All versions of this product (...) / Just this variant (...)". Similar to the way Apple segments mobile app reviews by release version.
