That is an interesting point you raise, Keith. When I first began preflashing, several years ago, I did just that, doing a test strip and choosing the preflash time just prior to visible grayness in the negative. But subsequent experience with the paper negative process has taught me that a well-exposed paper negative doesn't and shouldn't look like a well exposed positive print. That is, the paper negative shouldn't just be a negative version of the finished positive print.
The purpose of the paper negative, as with film, is to capture as much of the scene's tonal range onto the limited range available on the paper as is possible. My theory about preflashing is that the shadow detail of the scene has to be easily distinguished from the paper's otherwise unexposed whiteness. Preflashing raises the toe (shadows) of the response curve, without overexposing the shoulder (highlights).
I think it is possible to overdue the effect, excessively preflashing, which can cause the midtones to be muddy and lack separation. So there's a fine balance of giving the negative just the right amount.
I have lots to learn about this process. I really have not explored the possibilities offered by alternative developers, like the ones used to gain continuous tone images from APHS film, for instance (Soemarko's developer, IIRC). But working with paper is a real kick, and feels liberating, and gives more immediate results than sheet film (the paper can be easily rinsed and dried much quicker, and it only has problems of dust spots on the emulsion side, rather than both sides as with film). The downside is the lack or red sensitivity, hence its slow speed.
~Joe
I use Ilford MGIV-RC with a yellow filter (Wratten #8) and rate the paper at EI 3, but I don't flash or fog the paper at all. For development, I use Dektol 1+8 and develop to a Dmax around 1.2. The filter and the dilute developer control the contrast nicely.
