I always think of Crystal as basically reading the data, one line at a time, so it doesn't know about the output of a formula in the detail section in the header section...I could be wrong, but this is how I think of it.
To get summary info in the header, I usually have to create a formula that is an aggregate (get the sum of a field for a group) or if it is more complex, a subreport to report back the values.
Hopefully, someone else has an answer that gets the summary in the header.