OK...figured it out.
Oregon allows an OR income deduction for the Federal tax liability. Certain Federal tax credits are either allowed, or are not allowed to be used to adjust that Federal tax liability total that is eventually used to reduce OR taxable income.
From what I gather (if I see & interpret it right), Oregon does use the Federal stimulus payment you get, as reducing the Federal tax liability...thus a smaller OR income deduction (and more OR tax) when you enter the stimulus payments in the Federal section.
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The calculations that TTX "supposedly" uses are on pages 65 and 66 of the OR instructions...a series of calculations under "Federal tax worksheet" in the rt-column on page 65 and continuing to page 66. Step #8 in that series of calculations uses your stimulus payment to reduce the eventual (adjusted) Federal tax liability that OR allows you to deduct from OR income :
https://www.oregon.gov/dor/forms/FormsPubs/publication-or-17_101-431_2020.pdf
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
