1099-R Taxable Amount Not Determined

I'm a retired federal employee.  My 1099-R shows my gross annuity amount reduced by approximately 50% and paid to my ex under court ordered apportionment.  The taxable amounts were not determined.  After drafting and reveiwing my federal taxes with turbotax, I noticed that the Simplified Method Smart Worksheet calculated a non-taxable amount greater than the amount calculated and used in my 1099-R's in all the years since 2008.  This doesn't seem right even though it results in less taxes and would like someone to explain this to me.