Cupping makes a big differance in the sound of your playing. Even if you can't cup the entire harmonica, if you cup as much as you can the sound will still be a much fullier sound.

That makes sense. With my homemade mic sometimes I don't have the same sort of seal as without the mic. But even partial cupping makes a difference...

I agree, I've been playing for about a year now and I think that cupping and shaking has a definite wonderful blues feel.

I could not get a seal at all with a mic until I found on a web page another way to do it:
Hold the harp the no-mic way in your left hand, wrap your little finger and maybe some of your ring finger around the mic. Then use your right hand to cup in pretty much the no-mic way.