Why is this sql not recognising TargetPosition in IF statement

I have 2 tables with roughly the same columns.

I want to update the Status column of table Orders depending on whether the sum of ExecSignedAmount from table FilledOrders equals Orders.TargetPosition

But this UPDATE statement does not seem to recognise TargetPosition:

  UPDATE [FX_PROD].[dbo].[tblOrders] 
  SET [Status] =  (IF ((SELECT SUM([ExecSignedAmount]) 
                        FROM [FX_PROD].[dbo].[tblFilledOrders] 
                        WHERE [OrderID] = 2) = [FX_PROD].[dbo].[tblOrders].[TargetPosition]) 'YES' ELSE 'NO')
  WHERE [OrderID] = 2;

What am I doing wrong?