I didn't look at the measurements, frankly don't care about them. Any reviewer will tell you the measurements are a helpful tool, sometimes help explain WHAT YOU HEAR. but no measuring instrument catches everything the ear apparatus does. The W40 does indeed have a different sized nozzle; the body is also different in size/shape, slightly larger (I like the fit on the W4 better, to be honest, but can manage a fit with the 40 with some effort). Is this why it sounds better? I have no clue, does make sense it could. Now, do I care if you don't believe any of this, think the measurements are the be all and end all? Not at all. Different strokes, all that. I will say I own the W4, have the 40 on loan, strongly thinking of getting rid of the W4 and buying a W40 (have lots of other new iem's though, may hold off, got lots of good stuff to listen with). If you think it's all in my head, that's OK, that's where music enjoyment comes from. As I said, others, who believed as you do, that they are identical sounding from reading the posts, went out and listened to them after I posted I found the W40 better sounding, and agreed. One really should listen to the headphones before developing strong opinions on them, imo..hey, but that's just me, just have fun.