I use my Assos the same way and for the same types of rides as you. Even though it feels like you're sitting on a mega-diaper I never think about my bum after I'm well into the ride. One thing that I notice that may be more specific to me is that my base layer always seems to creep up and out of the front of my bibs. I don't think it's the base layer because it stays put when I wear my Castelli bibs.. It's annoying enough to make me think twice about getting more Assos bibs.