I had noticed that I got better ANR when not using my sunglasses, and realised this was due to the gap they were causing.
I bought a pair of those "stop gap" that are shown in the catelogues under David Clark Accoessories, and they helped a lot. Basically they are a small piece of foam, with a hole through the middle, which the stem from your glasses fit through. It then sits nicely between your head and the ear seal, and blocks the gap. Has made a big difference, but you do look a bit of a prat once you take the headset off!
Sorry, can't find a link to an online site. If you can't figure out what I'm talking about, I'll take a photo and put it up.
dp