PI chamois always move up on me as well. In other words, the chamois creeps ever so slightly from the front to the back and ends up out of place. I feel like I have a loaded diaper creeping out the back of my shorts..... (let the comments begin)

I just bought some Craft Dyanamic Bibs and they are the best fit I have ever had. The chamois fits perfectly and stays put. VERY comfortable.