Hi David,
The Report Header is executed before the Report Footer so you any formula that evaluates in the WhilePrintingRecords zone and accumulates values after the Report Header is printed will only show results in a later section.
To be able to show that result on the Report Header you need a Subreport (or even this same report inserted as a Subreport). A new Report Header b section can be inserted with the Subreport being placed in the Report Header a section.
You can suppress all the sections inside the Subreport (not the section that holds the Subreport itself) and place a formula in the Report Header b section that has the shared variable.
-Abhilash
