A1c is an indicator of what your BG has been 24/7 over a 2-3 month period. You A1c range you list is an average of 120-131 BG over that time period. Just to simplify lets look at that as being tested every hour and coming up with that number. Assuming you are testing 4 times a day (FBG and after every meal) that is just 4 of the 24 tests the A1c did per day for 60-90 days. You are probably looking at your highest readings of every day. But in reality your BG is constantly changing, and assuming it can change every minute, now you are looking at 4 minutes out of 1440 minutes per day, so actually a much smaller snapshot of what is really going on.
Most doctors follow ADA guidelines and recommendations and say 140-180 are OK numbers. However, there are studies that show that BG over 140 causes damage to nerves and organs. Click this
link to read about the studies I am referencing. There are links to the studies on that page if you would like to see even more detail. My goal is to try to keep my BG under 120 at all times for extra cushion, I don't always do it, but it is still my goal.