I wouldn't worry about any of that,
@Conor987 .
You're at 5.9 on waking, then you go for a 3 mile walk, your body realises you're doing a bit of exercise so releases some glucose from the liver to help you along with that, so you end up a bit higher at 6.7. Then you have breakfast and end up at 4.5 later.
But remember you had your 3 mile walk earlier and how your liver might have released some glucose to help out with that? It likes to keep stored up with glucose for future use, so it might have then taken some glucose back, dropping you back to 4.5. The liver both releases and takes back glucose.
There's a phenomenon called after-drop where sugars can drop substantially hours after exercise.
Of course, it might also just be that because you're not T, your body just did what it normally does and returns you to 4.5.
While we can measure carbs and bg quite easily, we can't really measure what the liver is up to. My DSN, who is T1 too, describes it as a, "sly wee f*ucker".
I'm looking at this from a T1 perspective but the basic biology holds true for non-T1s too.
On top of all that, agree absolutely with
@Jaylee ,s point that meters aren't like finely tuned scales. They give an indication of roughly where you are. If you get 2 readings 0.8 out, those are basically the same number for all practical purposes.