You can use tables to get the headers and images aligned, independently of font sizes:
[table][tr][td]Fooooooo[/td][td]Bar[/td][/tr][tr][td][size=8pt]Foo[/size][/td][td][size=20pt]Baaaaaaaar[/size][/td][/tr][/table]
I tried tables. Let's just say it didn't work too well. Something about the SMF code does nasty things to the layout when you're working with images in tables.