To balance the effectiveness (retrieval of the nearest neighbor) and the efficiency (complete the process within limit time) of the retrieval, some empirical tricks are usually applied in previous search on graph methods: a) use directed edges instead of undirected edges; b) restrict the degree of outgoing edges for each node; and c) select more diverse outgoing edges (Malkov and Yashunin, 2018; Morozov and Babenko, 2018).
for the inner product case, ip-NSW proposed in (Morozov and Babenko, 2018) applies all tricks listed above (although the authors did not mention it in the paper, the implementation did inherit all features from HNSW).