Form 2210 Schedule AI Applicable Percentage

Can someone explain where the pre-filled applicable percentage on line 10 of form 2210 Schedule AI comes from? See snippets below. I think the IRS takes 90% of the period and puts the % there. For example, column (a) is 3 months. That is 25% of a year. Take 90% of that, and you get 22.5%. That checks. It also works for column (d). However, column (b) doesn't work. (b) is 5 months. That is 42% of a year. 90% of that is 38%, but the IRS pre-fills in 45%. Same issue in column (c). The result is columns (b) and (c) will artificially tell you to pay more than you really are supposed to. Someone tell me if I have this wrong. Thanks for the help. 

 

 

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