Hi Jon,
When mixing wet and dry dog food, you have to always reduce the amount of the previously fed (in this case the dry) in order to not provide more calories than they need. There are no set ratios or amounts of wet to dry food. It would be best to ask your veterinarian or veterinary technicians to assess the body condition score of Blue and help you determine a calorie amount he needs per day. Bring the foods with you so they can do the appropriate calculations. Many veterinary clinics may do this at no cost to you. For more information about this topic, I encourage you to watch our video about food recommendations for dogs.
All the best.
Dr. Ryan Llera