The 6 inch one rides up like crazy, I can only imagine what the 3 inch would feel like. The 9 inch pair I have is absolutely perfect and doesn't ride up at all. I VASTLY prefer my 9 inch to the 6 inch, and imagine it'd be preferred even more above the 3 inch.
i've tried the 3 inch, and they ride up like CRAZY. the fabric does feel amazing, but they fit pretty loose for boxer briefs and I found myself having to adjust them (make sure no one was looking and pull out the fabric wedged in my crotch) after every time I sat down.