Thanks, Steve. It's been months since I did any pinhole, I really do need to do more.
About the paper I use, it's Freestyle's Arista brand in grade 2 glossy RC. I prefer grade 2 over multi-grade for better control of contrast, and the paper is not contrast sensitive to the color of daylight, as would be the case with MG paper. Through calibration tests I've come to rate this paper at an exposure index of 12, with the caveat that the dilute developer has to be up to proper temperature (at least 68f), and that I develop for at least 2 minutes.
The camera is a plywood 4x5 camera at f/280, takes standard sheet film holders. Bright sunny morning, plenty of light.
My exposure method is that I meter the scene at ISO12, select the exposure time for f128 on the meter, then do the conversion to the camera's focal ratio of f280. Part of the calculation is already done previously [(280/128)^2=4.78] and is applied to the camera as a label with the conversion factor of 4.78, such that all I have to do is the simple multiplication after the meter reading. All of my pinhole cameras are labeled with their conversion factors, which makes it very easy to shoot in all kinds of light, since paper has virtually no reciprocity failure.