Many formulae for optimum pinhole diameters are most valid for on-axis image sharpness. However, both sharpness and illumination dramatically decrease near the edges of ultra wide angle coverage. A somewhat larger than normal pinhole can provide some gain in corner sharpness at the expense of on-axis performance. 30 years ago I improvised a camera to test this. A rough graph of the results is attached. Also, in regard to filters, since the sharpness of pinhole photography is partly dependent on the wavelength of light, there is a very slight gain in sharpness by using blue sensitive film or a blue filter over using a red filter. This, too, has been verified by experimentation, but I don't have the results available.