If he's 1,270G, I would not be feeding him medium rats. He will do better with small rats every two weeks. Easier to digest and he will be less likely to go on hunger strikes, etc.
My 2kg female BP eats smalls every two weeks and aside from shed and her winter fast, eats like clockwork and is healthy. She loses a little weight in fast (about 5 months of fasting) and then gains it all back quickly in the spring/summer.
BP's are super efficient and do well with smaller, but appropriate sized meals. I often remind BP owners that in the wild they eat mostly African Soft Fur rats (ASF). They average about the size of the small rats we get at pet stores or order Frozen from suppliers (60-90G).
Thanks so much for this information! I will try introducing small rats after antibiotics are done.