A recommender ranked mostly by distance raised add-to-cart rate but lowered revenue per session: diagnose why and design a replacement with experiments to separate causes.

Sorting by distance favours cheap, nearby items, so carts fill more often but with smaller baskets. Decompose revenue per session into conversion times order value and slice by category and price band to see which term moved.

Replace it with a ranker scoring expected revenue: relevance times conversion times basket value, with distance as one feature. To separate causes, A/B test old, new, and a distance ranking reweighted to the old price mix.