I'm not convinced that Carapils actually does much of anything in the amounts that people typically use it, 5-10% or whatever.
I totally agree. I put carapils in the same category as flaked oats...in theory contributes something, but in reality it doesn't seem do a darn thing, at least in my brewery. I never use it anymore.
Edit: However, if using a diastaticus strain that strips out all the dextrins, I can see how a small amount of any grain, including carapils, might be noticeable. Once you get rid of all the extraneous noise, the signal becomes more visible.