FWIW, I typically skim, but if I see some green color, I will stir it in and then skim when all is tan or without the green. However, I use stainless mesh canisters or a hop spider stainless mesh thingy to contain the hops somewhat. That alone may be affecting the calculators, hence my seat of the pants ultimate hop use determination. I am less than scientific on hop measurement, since I am typically very low on the IBU's anyway and as I understand it, the IBU measurements may have been very "testing equipment dependent" in their original development...