Using spatial fields in an expression in Report Builder

I have a report (made using Report Builder 3.0) using a map based on an ESRI shapefile. I changed the layout tooltip to #name (the field linked to outcode) so when I hover over an area of the map in the preview it shows the relevant outcode. I'd like to add the count to that tooltip as well, but can't get it working. I've narrowed it to a problem using the spatial field in the expression.

Is it possible to use spatial fields in expressions? If so, how do you reference them?

Here's what I've tried so far:

=Fields!name.Value & ": " & COUNT(Fields!OUTCODE.Value)

=Fields!#name.Value & ": " & COUNT(Fields!OUTCODE.Value)

=#name & ": " & COUNT(Fields!OUTCODE.Value)

This one works, but if there are no records matching an area, no tooltip appears:

=Fields!OUTCODE.Value & ": " & COUNT(Fields!OUTCODE.Value)

Thanks!