I think they are looking at it from the wrong end, I believe it is carbon coming back from the combustion chamber, as the intake valve opens. Similar thing happens in direct injection motors as the petrol isn't cleaning the runners.
It is not in the flow path as the ethanol pushes that out the way. The modified 1000's are actually good for this, as the tip isn't large enough to gunk up too much. I doubt there will be a flow difference unless the filter inside the injector is blocked.
Those 1000's I mentioned above had a little filter added in the top, which was the likely cause of the flow issue he had. I never run those little secondary filters anymore, they are too fine and block up easily.