Pre tax Account Characterized?? Turbo Tax Premiere Home

I participated in 457B plan  thru a prior employer.  8 years ago, after retiring, a qualifying event,  I took one $75,000 distribution. It was drawn over 3 successive years at $30,000, $22,500, $22,500. The balance of the 457b was then directly rolled over into an IRA account opened with Fidelity.  Fidelity was also the custodian of the 457b .  So the 457b became a Rollover IIRA .  Since then additional sources of qualified pre-tax revenue has been added to this same account.  This year, the 2024 tax year, 8 years later, I am performing a 4th successive partial ROTH conversion, $50,000, from that IRA account.  When I characterize the originating account as an IRA, in Turbo Tax Michigan, I receive a $1500 state refund (I am employed and pay state tax thru payroll.). When I characterize the account as a 457b the tax software indicates $500 of state tax is owed. BTW I am 64.5 years old.  Which way is the proper manner to enter the pre-tax account type from where the Roth conversion funds are coming out.   Should it be characterized, as a 457b or an IRA?