While the amount of thought and figuring that went into this is commendable, it's a bit over done. Allot of math breaks down when it hits real world conditions. Diffuse source for contact printing is fine, but you can't see or control dodging or burning. The glass is there not just to press for sharpness, but to assure absolute contact, to prevent Newton rings, which is what you will get, sooner or later without the glass, depending on the negative, humidity, and other factors. An enlarger makes a wonderful light source for contact printing, particularly a dichro head, for split printing. The lens aperture matters not a wit, with a good frame, and a miniscule aperture would do little except give unbearably long exposure times. Use a good quality contact printing frame with clean scratch free glass, and strong springs, throw away the slide rule, and print away.