Thanks, Bruce
That would work if the 'always' field was normally the bottom of the page. Otherwise when the 'sometimes' field isn't present, the next field is brought up to the same line as the 'always' field which would be very confusing for the user (the fields are not related).
As I said, this is an aesthetic, intuitive issue. The functionality is fine. But if it isn't a lot of work, a conditional last on line property would be useful. This isn't the first time I have encountered this issue.
Thanks again.