Final answer:
The optimal degree to tilt an obese decedent's head in a casket is not provided in the reference material and is usually determined based on the specific circumstances and family preferences.
Step-by-step explanation:
The question concerning the positioning of an obese decedent in a casket doesn't have a standard answer related to angles as found in the questions provided from Physics or Mathematics. It's a query more specific to mortuary science and the practice of funeral services. The optimal degree to tilt an obese decedent's head in a casket is not established in the provided reference material. However, such decisions are typically made on a case-by-case basis and take into account the specific physical characteristics of the decedent as well as the preferences of the family.