I almost spent over $200 on 12" above the lens Ilford MG filters for my 8x10 enlarger based on that "above the lens" dogma. If you read the instructions for the smaller Ilford MG filters it says it is ok to use them under the lens, and I can say that indeed that is the case. I wound up getting the six inch below the lens filter set and saw no loss of quality (with grain magnifier and in prints) using the filters below the lens.