Imputed Income Question Domestic Partner - Texas

Are there any special calculations for calculating the federal withhold on imputed income. I'm trying to recreate the withholding calculations for a paycheck, and it doesn't seem to line up with the 15-T bands.

 

For reference:

 

Biweekly pay: $3,692.31

Imputed income: $1,098.89

Pre-Tax Deductions: $506.33

Federal Withhold Paystub: $578.50

Federal Withhold Calculation Using 15-T: $628.86