Type 2 learning about a CGM

So, I have been persuaded by my doctor to use a Libre 2+ CGM. I put it on and find there are three main spikes in the day, as expected, and saw that my evening units were not doing much to my evening food. I do the injection 15 min before eating, the BG rises for about 3 hours, and then spikes for another 1.5 hours before settling at about 13.5. The the only way to get it down is to do about 3 units of fiasp which brings the number down to BG 7.5. So my question is is it normal for digestion to continue for 4.5 hours, and does fiasp work for 4.5 hours.

Hello @Lakeslover , I have not found a way of calculating the number of units, I just wind up the pen till I see the BG at a good level, and the 25 units I take in the evening is not doing that. My regular evening readings are 11 - 15.5, which I correct with a 3 unit shot just before bed. It all goes down overnight and is ok in the morning. But I am not sure if the three unit shopp is the best way of dealing with it

hello @Lakeslover yes originally I tried calculating a dose base on how much carb there was on the plate, but found the amount of insulin changed dependant on what the carb was, and I could not find a simple units ti carb ratio. It seems to depend more on how quick the food is digested. So as breakfast is all digested in 2 hours I give it 15 units and lunch does not cause a spike, 15 units, then 25 for eveneng meal which digests for about 4.5 hours and always is left with BG high.
My doctor has said my units of fiasp are ok and A1c is ok, but when pressed for a number she said everything is good, wear the CGM sensor.

Hello @Lakeslover yes I can imagine alcohol delaying BG rise, but I saw that alcohol does not go well with diabetes, so I decided 9 months ago to cut all alcohol out of my diet. I am not so much a reformed alcoholic, rather a person who looks carefully at whats actually in the diet.
It is this idea of taking insulin an hour after food, or doing a second correction dose of 3 units if the spike does not go down after 2 hours, that I am concidering. My time in the green on the CGM shows 87% for the first 7 days of using it, so I am sure I have some kind of control. But spikes occur, between 3 and 4 hours after the evening meal, and will either come down overnight, or be brought down with a 3 unit dose before bed. Either options give me a about 1 hour in the red, lower than 3.9 between 3 - 4am.

Hello @Antje77 yes I did try moving the dose to 30 min before eating and that seemed to reduce the spike at breakfast, so I am adopting that for the start of the day. But the evening dose just seems to run out of effectivness and the spike just rises hours after the meal with no little snacks in between. It was not a problem before the CGM, as I did not test in the evenings, but I knew it was often too high before bed, but always just right in the morning at 6.2.