Hi @clement and @Michael_Edgett, and thanks for your suggestions. They both work in some cases and not in the others. Adding vectors on top of each other (from main point to start-end) gives good direction at the top of the pyramid, but the 2.04 length is not correct. Also, at the base of the pyramid (3 surfaces only) - both direction and length are way off. This method works nicely with a corner of a cube though. So I still can’t figure out the perfect rule for that and I do realize now that with some more irregular shapes there is no obvious 1-point solution.
I had more luck with the plane interserctions that produce correct result in both cases of the pyramid (top and base) and a corner of a cube - in these cases, I create planes from normal vectors, offset them by vector length=1 and run Rhino.IntersectPlanes using any of 3 adjacent face planes - the result is a point that connected with the corner point creates a correct vector direction and length. Since in my case 99% of cases will have 3 adjacent surfaces only I think I will stick with that method.
Thanks again for your help!
–jarek