Your goals and logic regarding normal blood sugars after 4 hours are basically sound.
The idea behind a test @ 2 hours after eating is to provide a gauge on how well you bolused (and possible how well you are digesting the food) for the meal. With a 4 - 6 hour activity, NovoRapid has a peak activity of something in the 30 - 45 minute range, so @ 120 minutes, there is not 50% remaining, but more 20 - 25%. I would still agree with you that if you started a meal @ 5.5mmol (100mg/dl) and tested two hours later @ the same level, you will be headed for a low. That is part of the purpose of the test, then. If you are @ normal level two hours after eating, you probably need to eat additional fast acting carbs to prevent a low. Similarly, if you are 11.1mmol (200mg/dl) at two hours after eating, you might want to consider a correction bolus, because the remaining NovoRapid is unlikely to get you to normal in 4 hours.
By checking two hours and four hours after your meals you might be able to spend more time “in range”. Avoiding lows and long periods of highs - IOW, increasing time in range, will likely result in a lower A1C.
Here is a link to the “Mechanism of Action” for NovoRapid.