Originally Posted by notimp
If ixtab doesn't find a way to circumnavigate the problem
AFAIK, nope for the AZW3 reader which doesn't rely on the java framework Ixtab has found a way to inject code in. I don't know if it's possible for the mobi reader. But - maybe - at least he can understand why Amazon does not want us to use certain font sizes.
Another option could be to hardcode the font size within the book stylesheet itself (never tried, however).