Conditional Font Size in Custom Header

Has anyone worked with conditional font sizes in  a custom header?

I'm trying to make it so that if full_name is longer than 35 characters the font size is smaller than it otherwise would be. I got it working in infomaker so that when I preview it, shorter names look exactly the same size as they always were, and longer ones are indeed in a smaller font. But when I log in to Tessitura with the user group that uses the header in question, the long names still look the way I wanted them to, but all other names are showing about double the size of what they looked like in the preview. I adjusted the size down so it's normal in the application, and in the preview now it looks shrunken. It's not really a big deal since I got it to look the way I wanted eventually, but now I'm puzzled.

Has anyone experienced this? Any ideas?