Fill up values: Multi Row formula tool does not work?

I am trying to fill up the Site Name column however the formula is not working as it is supposed to.

Formula:

IF ISNULL([Site Name])
THEN [Row-1:Site Name]
ELSE [Site Name]
ENDIF

What am I doing wrong?

Please find example workflow attached.

Thanks

Workflow

Help

Accepted answers

I think we need to do a sorting first, to bring the non-null value for site name to top, then the multirow formula will work.

I think we need to do a sorting first, to bring the non-null value for site name to top, then the multirow formula will work.

Yep, that works however why would the fill up formula not work?

What you have provided is a fill down solution and I have a use case for a fill up.

Thanks