I am proposing to use Ilford Harman Direct Positive paper in my half plate camera.

Does anyone have experience of doing this? If so how, and for how long, do you pre-flash the paper to reduce the contrast, prior to the main exposure?

I have read the information sheet produced by Ilford Harman, but this is not making much sense to me! The notional speed of the paper is 3 ASA. Is there a formula to decide what % of the metered exposure should dictate the pre-flash exposure time?

Kind regards,