Quote Originally Posted by DREW WILEY View Post
Forget the blue filter thing and the nonsense that spacing at the easel doesn't matter.
It is nonsense that it does matter.

If you think the difference in paper thickness at the base board makes any difference, try to work out how small a change in the negative to lens distance would need to be in order to change the focus point by the paper thickness (or even by 2mm). It is a few microns. You cannot adjust the focus of an enlarger that accurately.