Masking film emulsion up or down when creating unsharp masks?
I'm just starting to explore the world of mask-making for B&W printing purposes. My questions pertain to correct technique for creating unsharp masks.
Fig.1 on p.257 of Ralph Lambrecht's most excellent "Way Beyond Monochrome" (Ed.2) indicates that when creating the mask (i.e. not printing) both negative and masking film are placed in a "sandwich" with both films emulsion up.
Fig.2 in Mark Jilg and Dennis McNutt's article "Three Contrast Reduction Masks" indicates that when creating the mask both masking film and negative are placed in the "sandwich" emulsion down. Similarly, Howard Bond's article in the Jan/Feb '96 edition of "Photo Techniques" indicates emulsion down.
In short: why the difference and does it matter?
I appreciate that if the masking film is a thin base film (e.g. ortho-litho) used emulsion down without a spacer then the degree of "unsharpness" will be severely restricted on account of the thin base of the masking film. By contrast, placing both emulsion up means that the degree of "unsharpness" is always at least that due to the thickness of the negative base.
Does this explain why Lambrecht (who is chiefly interested in sharpness effects) recommends emulsion up and Jilg/McNutt (who are more concerned with contrast reduction than sharpness) recommend emulsion down?
Any other pros and cons to either approach that I'm missing? Comments appreciated and thanks in advance