ProZinc hits its lowest level about 5 1/2 hours after a shot. Go with the same dose (1.5), and check at + 5.5 to see how low he goes; that will help determine if he needs more or less.You want his lowest glucose to remain above 50 mg/dL. About 3 doses at the same level of ProZinc will give you a sense of whether or not that dose is good for him or if it needs tweaking
Also, it is very common for a large drop or a lower value that what has become habitual, to trigger compensatory hormones that release stored glucose (glycogen). This is called a bounce. The high number you are seeing now may be a bounce.