The occlusal rim in the molar region should be positioned slightly lingual to correspond with the natural position of the mandibular teeth, which are set slightly lingual to the alveolar ridge. This placement helps in achieving proper occlusal relationships and muscle balance during denture fabrication. Positioning the rim too far buccally can lead to instability and improper occlusion, while placing it directly over the ridge ignores the anatomical lingual inclination of molars. Ensuring the rim is slightly lingual facilitates correct vertical dimension and occlusal plane orientation, critical for effective mastication and denture retention.

Reference: Prosthodontics: Principles and Management of Edentulous Patients, T. E. Phillip, 12th Edition.