If you ate nothing at all for a few days, your BG readings would drop down to around the 4.0 mark and then your body would create new glucose from stored lipids to top you up. Your BG readings rise again. Its the rate at which they climb, how high they climb and how long they take to come back down which determines whether you have diabetes or not.
You can overmedicate and your BG can go too low but its generally not a problem for type 2s on metformin. It's more a problem for people taking very strong meds or insulin who overmedicate.
Metformin doesn't really even things out in the way you mean. What it does is slows the rate of digestion and hence the rate at which glucose is released and helps your body's sensitivity to insulin. It's all about the top end of the range, not the bottom end. For most type 2s, the bottom end sorts itself out.