Amethyst's nadir is late in the cycle on Levemir. It's natural that she would go lower later in the day, in spite of eating. Many Levemir kitties nadir around the next shot time. Plus she could have some IAA action going on - antibodies can release stored insulin at the most inconvenient of times. When Amethyst's dose is a bit too high, it seems she likes to nadir quite late in the cycle.
As Julie suggested, I would experiment with different high carb foods. Some cats (acro or not) need higher high carb, maybe 25% carbs food. Some need less - most of the time I could get away with 16% carbs with Neko. But if she went below 40, out came the syrup (karo).
It will really help you to put comments in the Remarks column as to what time you give extra food, what carbs and amount. For example, when you saw that drop to 65 @+8, I might have given her some higher carb food to see if I could stop the drop, knowing she still had 4 hours until the next shot time. Once you keep track of the data on your spreadsheet, you'll get a better idea of what food works and when. You want to avoid having to miss shots, cause it makes it harder to figure out what dose she should be on.
As for new dose size, I would try 6.0 units again. Even though it didn't do anything this time, it might work this time.
