libreoffie calc macro to paste formula

Question

I want a macro to paste a standard Libreoffice formula. The formula is: =IF(D13<>"",VLOOKUP(E13, $Jnr_ranking_processor.$C$11:$G$50, 5, 0),"")

I have a Form Control button to trigger the below macro.

Sub AssignFormulaToCell
' Source: https://help.libreoffice.org/latest/en-US/text/sbasic/shared/calc_functions.html
REM Add a formula to cell I13. Function name must be in English.
    oCell = ThisComponent.Sheets.getByIndex(0).getCellRangeByName("I13")
    oCell.Formula = "=IF($D13<>"",VLOOKUP($E13, $Jnr_ranking_processor.$C$11:$G$50, 5, 0),"")"
REM Cell I13 displays the localized function name
End Sub

When the button is pressed, I13 reports "TRUE" Why? The 'raw' forumla before using macros gives the actual lookup value.

This macro needs to be pasted into from I13 to I43. How to get the macro the row for D and E in the vlookup to be the same as the row where the macro is to be pasted. Surely one doesn't have write in effect 20 macro's with each one having a manually adjusted row. {I'm not sure how to write a for loop with an iterable in a formula.}

Thanks for any help/advice offered.