It's even less, about 5 mm, (3/16") in circumference. (Circumference being a combination of left to right as well as top to bottom.
Watch out, not every width reduction reduces the width left to right. Two or maybe even three width might be built on the same insole (to save production components), just reducing the height top to bottom. Probably between C and D there is a reduction from left to right, but between D and E there probably is not, the E is just higher.
I would say, AA and A (extra narrow) are on the same insole, as are B and C (narrow), D and E, EE and EEE. But that varies from manufacturer to manufacturer. With each increase in width the total circumference increases.