From what I understand, the amount of adult hemoglobin that becomes glycosylated to form HbA1c is directly related to the average concentration of glucose
in the blood
. In a normal person about 3-6
% of Hb is glycosylated.
One thing to investigate is whether you are experiencing the Symogi effect [reverse hyperglycemia while sleeping]. To counter this the liver releases extra glucose. One way to find out is to set your alarm and wake up at 2-3 am, or 4 hours after your bedtime, and test.