Currently, ProximityPrompt.RequiresLineOfSight does not respect bounding boxes for Model instances and can result in the ProximityPrompt not showing up for geometry blocking it within the same model.
The only workaround to this that I can think of is to have a constant raycast between the model and the character with both models being ignored. It would be more useful to have
ProximityPrompt.RequiresLineOfSight respect the bounding box instead of just the pivot of Model.PrimaryPart.
If you ever want the old behaviour; there is always the option of using Attachment inside of parts. I do not think that this changed behaviour will break any games, but if you think it will, please tell me!