I assume that's with the focus of your lens manually set to the minimum distance? Changing the focus of the lens should still have an effect though, even with the attachment on
Other than that, you can try using higher F-stops and long exposure like I mentioned, so you get a larger focal plane at least - though I am not sure about the progression from the focal plane to out of focus areas, it's possible those things you want blurred will appear a little
too defined. Trial and error, I guess