Adjusting GuiMLText Font sizes in different resolutions

I'm having trouble trying to figure out how to set the GuiMLText font sizes in different resolutions. I tried using global variables for each font size that I want to use. I set them up when the game starts based on the variable $pref::Video::resolution. It doesn't seem to work and I wanted to know if anyone has tried another way, otherwise I'll keep on working on it. Thanks for any info.