Fine-Grained Preference Optimization Improves Spatial Reasoning in VLMs - Shen, Yifan; Liu, Yuanzhe; Zhu, Jingyuan; Cao, Xu; Zhang, Xiaofeng; He, Yixiao; Ye, Wenming; Rehg, James; Lourentzou, Ismini (Advances in Neural Information Processing Systems, 2025)