Need to Add Invoice table OINV to Collection report

I have added a field to the Invoice table OINV and wish to display it in with the Collection Report.  SAP Modules->Financials->Financial Reports->Accounting->Ageing->Customer Receivables Ageing -> report AGE30001

The invoice DocNum field is in the Reference Text field in the Repetitive Area Field F_034 as IN 12345

I have created a field F_222 as a formula field  with the formula ToNumber(Substring(F_034,3,8))

This gives the correct number 12345.

I have then created a new database field AR Invoice:Document Number, Table AR Invoice and Field Document Number.  I have set Relate to to F_222.   and next segment is blank.  This displays the number 10008 which is meaningless to me.

In general should 'relate to' be a field that in a sql statement would be expressed by 'join OINV on DocNum=F_222'

What does 'next segment' do as normally if you have subsequent clause it is 2 different fields.  I have been unable to find the documentation on this aspect of PLD reports.