Bought this for my older dog to use during our hot Kootenay summers. She has a lot of fur, so to improve performance, I shaved her belly for good contact between the cooling pad and her belly. The "vest" concept also helps to provide pressure on her body, which asks a bit like a thunder fest. Shes reactive to people out of anxiety so this seems to help with that!
Her thick coat does make her look a bit like a bulky sausage but I wouldn't suggest going a size bigger since I think you want decent contact to ensure water top ups properly soak into the undercoat.