I see what you mean, but do you think directly under the lens or 1/2 inch below the lens makes a difference?
I suppose it could make a difference if printing 5 x 7 's compared to printing say 11 x 14's because as we all know, the smaller the print the closer to the paper the lens is. When I was learning the fundamentals I had it lodged in my brain that the space between the lens and the paper was sacred. The only way to find out definitively would be to test, scratch a filter and see if it is noticeable on a print when the filter was 1/2 inch from the lens compared to up against the lens. For me its a moot point as I've always printed with a colour head and never had a need to print with a filtration other than what the colour head could deliver.
It is said that we remember the important things, if true, why photograph? I forget, so I photograph.