This is taken from the Study Guide for API standard 1104 20th Edition

Question 11.8

What is the essential diameter required for the radiographing 0.750 inch steel with an ISO IQI?

The correct answer is

C. 0.016 in [0.41mm]

My issue is, I selected  answer

B. 0.020 in [0.51mm]

Table 6 - Weld Thickness versus diameter of ISO wire IQI (page 33 of the 1104 study guide)

>0.500 - 0.750 inches  Weld Thickness       which gives the answer  C   0.016 in [0.41mm]

>0.750 - 1.000 inches  Weld Thickness       which I thought was the answer, and I selected   B  0.020 in [0.51mm]

Based on what I see, I should go down the thickness range?  I know the test are notorious for giving more than one correct answer, one being more correct.  Any explanation for the selection of the answer is appreciated.