Presumably you mean cataphasis rather than apophasis? ~ the differenc between affirmation and denial. I share the regular puzzlement over these niceties of rhetorical figures: the examples offered don't always seem to me to well illustrate what the speaker claims they do.

The pair of cataphasis and paralipsis I understand to be really just a mattter of degree of emphasis: cataphasis merely states whilst claiming not to so do ("I will refrain from mentioning my opponent's diminutive stature"), whilst paralipsis seems more ironic in tone ("it would be cruel to draw attention to my opponent's diminutive height, which clearly has no bearing on his wish for smaller doorways").

Fong's pair are a typical example of classifications that, not only do I not remember the difference, but even when I look 'em up again I can't see clear water between!