A wrist-worn vibrotactile interface was previously studied but was aimed at low-resolution navigation tasks such as driving. The previous design had achieved up to six directions for three-dimensional navigation. We argue that the expressivity of vibrotactile navigation on the wrist has not been fully explored, and we address how three-dimensional direction cues can be packed into a wrist-form tactile interface. We present an 8-tactor cuboid worn in wrist form to generate high-density three-dimensional direction feedback around the wrist. This sparse arrangement of 8 vibrotactors allows up to 26 directions to be presented, when benefitting from phantom illusion. We conducted a study with 36 participants to inform the effective design of the interface regarding two factors: the cuboid shape (e.g., the length along the wrist), by comparing 4-cm, 6-cm, and 8-cm configurations, and the direction feedback, which includes point stimuli and motion stimuli. The results show that 6 cm strikes a balance between form and recognition rate. The direction feedbacks made with motion stimuli (80.2%) are generally more discernible than those made with point stimuli (69.6%).