Is column visibility based on the first page of the result set or the entire result set?

I have tried, in vain, to play with the column visibility expression in my report. So where my Business Unit is "MC" or "FM", then I want to display column "HCFA Number"...otherwise hide it. If I run strictly for "MC" it works! If I run simply for "CO" it works! And doesn't show! But if I combine "CO" and "MC", it is hidden and I would expect it to be visible since "MC" is part of my entire report.

Here's the expression I came up with for Column Visibility...

=IIf((Fields!BUSINESS_UNIT.Value = "MC") OR
        (Fields!BUSINESS_UNIT.Value = "FM"),FALSE,TRUE)

Am I missing something here or just being dense late on a Friday???

Thanks for your review and am hopeful for a reply.