Power Query custom function variable to make table a list

I have the folloing custom function, but the last part [Units] I would like to put as a variable ,

( mytable as table, mycol as text ) => 
let
    Custom1 = Table.AddColumn (  mytable , "NEW", (A)=>
List.Last( 
  Table.SelectRows( mytable , (B)=> 
  Table.Column (B, mycol )  < Table.Column( A, mycol)  ) [Units]  )   )  
in
    Custom1

Just trying to add it 'toList' as text and then adding it directly does not work nor does TableColumn ,

 ( mytable as table, mycol as text, mylist as text  ) => 
let
    Custom1 = Table.AddColumn (  mytable , "NEW", (A)=>
List.Last( 
  Table.SelectRows( mytable , (B)=> 
  Table.Column (B, mycol )  < Table.Column( A, mycol)  ), Table.Column(mytable , mylist)  )   )  
in
    Custom1

Is there a way I can not have this part hardcoded. Attached workbook with several attempts.

Richard.