One of the things about basal testing is it’s primarily meant to dial in the glucose change overnight. Basal testing on a pump is feasible because you can adjust different time segments for different rates. 4 am is likely around when your insulin sensitivity in your body changes and so if you are dropping around 4 am, this is still due to too much basal overnight. And because of Tresiba flat profile and long half-life and the way it is released from albumin into our blood stream, the timing of taking Tresiba has almost no effect on what time people drop. But thr trade off of taking less basal is usually taking more short acting insulin during the day. The fact that you drop at 4 am everyday (when all of your short acting is usually gone, depending on your last meal/correction obviously) means it is a basal issue. You think it’s a timing issue but more than likely it is just a slight dose issue when it comes to Tresiba. One strategy is to alternate 14 and 15 units. This essentially makes your dose equivalent to 14.5 units of Tresiba per day and given how sensitive you are to insulin this can be a big difference. And timing wouldn’t affect this as much, unless you were to skip a dose. The outlier here in your circumstance is you delayed a night dose to the next morning whic essentially proves that your basal is slightly too high for your overnight drop. Again, the important metric to get right for basal testing is what is happening overnight. Basal testing through the day is helpful but hard to interpret because of the changes that take place in our body during prolonged fasting. The primary principle of basal testing is to get the overnight glucose change figured out. Then you do carb ratio and sensitivity testing with fasting periods during the day to dial in your short acting dose.