If you use it every day it will eventually swell in diameter to fit the bowl as it absorbs moisture. All soaps do this actually, so if you've ever been annoyed at those ill-fitting wooden bowls this is also the secret with them. The quality of the soap lather improves as this happens, so when you find a soap you like stick with it every day until its gone for best results.
As for MWF, I love the bowl but hate the soap. Doesn't matter what I did or what kind of lather I made - thick, watery, airy, whatever - when it came to the shave it felt like I was shaving through elmer's glue. My suspicion is it's the lanolin reacting with something in the water or my skin. I wound up digging out the MWF and tossing in an upside-down puck of Harris Arlington, which neatly solved the problem.