State tax filing

Thanks, I entered into line 23 of schedule C. I had it before as a separate custom line "State Excise Tax". My question is, any deduction in this form is against your income tax based on you tax bracket, while the state excise tax I paid should be deducted from tax directly as $ to $ not % of that.

For example: I own $4000 tax and I paid $2500 excise tax. thus I should paid $1500. But the line 23 only deduct 20% of $2500 = $500 from $4000

Am I wrong?