Your recall@50 is 0.58 and a teammate proposes query ex...

A strong answer distinguishes between lexical, semantic, and signal-based expansion families. It notes that since expansion creates a superset of documents, recall is guaranteed not to decrease. However, precision is only maintained if the newly added documents are relevant at least as often as the existing top-ranked documents. One must also analyze the specific cutoff (e.g., k=50 vs k=5) because the effectiveness of the expansion changes drastically depending on the depth of the retrieval list.