This section of the forum is intended for reporting possible bugs with software from the FileMaker product line. Questions on how to use FileMaker should be asked in the FM Pro Forum. (and questions asked in that forum get quicker answers from more people too.)
Define this relationship in Manage | Database | Relationships:
Table1::InputIncome > Deductions::minincome AND
Table1::InputIncome < Deductions::MaxIncome
And use it for your looked up values.