I believe there's a thread over on F295 where someone went and calculated what the actual off-axis focal ratio and light falloff would be when taking into account a pinhole made in an actual material of finite wall thickness which, when viewed from an angle, appears to be elliptical, due to the real-world wall thickness of the pinhole material.
It's a great exercise in geometry and math, but really doesn't effect my personal pinhole photography, which I do by imperical testing rather than through calculation.
As for an "acceptable" angle of view, this is really an aesthetic choice that an online spreadsheet can't decide for you. Some people like the "Holga-like" dark corners, or whacked-out extreme wide-angle views, while others like their images more serene and even-exposed from center to corner.
I think it's an interesting technical challenge to determine all the parameters of a pinhole camera and image ahead of time, but that doesn't really make us better photographers, nor do such calculations inform us about aesthetic choices that only we can make for ourselves. The great thing about pinhole photography is that there's no "right" or "wrong" approach, so the idea of hard, fast, fixed rules is a misnomer. Sometimes the best pinhole images are the ones resulting from the most spontaneity, with the least amount of preplanning.