I can only speak from a couple of months experience... but there isn't always logic to blood glucose levels. It just depends how much or how little insulin your body has managed to release.
For me, as a newbie who is on an extremely low carb diet, either of your figures would be a great pre-lunch reading for me. I can eat exactly the same thing, do the same amount of exercise on two days, and can have a reading of 5.5 or a reading of 9.5.
Not sure how much metformin you are on, but I'm on 2000mg. I was told to take 2 x 500mg at breakfast, and 2 x 500mg with my evening meal. However, I've found that by splitting my dose up and taking 1 with breakfast, 1 with lunch, 1 with dinner, and 1 before bed, I maintain better control. It may be worth discussing it with your DSN/GP.