Can you do a without diffuser and with diffuser picture comparison to show us the difference? Have you tried the light meter for android to see what kind of lumens the light is putting out and different distances? Would be interesting to get some numbers if you have a phone and the time to do some experimenting. Could do similar to how you did the x distance from wall comparison, but tape the phone to the wall and see how different lights compare. Here is a link to the software if anyone is interested. Would also be interesting to know how much light is being soaked up by the diffuser, theres always some energy lost to devices like that!
https://play.google.com/store/apps/details?id=spaceware.lightmeter&hl=en