[amsat-bb] When exactly is a non-conductive mast necessary?

I'm trying to understand, under what circumstances is a non-conductive mast necessary at VHF/UHF frequencies. Thinking of the following installs.

1.  Circular polarized antenna mounted to the mast at the center of the boom.    This is clear, see this advice all the time, fiberglass mast.

2. Same antenna but mounted at the rear end of the boom.

3.  Vertical Yagi, elements parallel to a vertical mast, mounted at the center of the boom. I guess, non-conductive wold be required here.

4.  Same antenna but rear mounted.

5.  Horizontal Yagi, elements perpendicular to a vertical mast, mounted at the center of the boom.  I think this is pretty normal install, so a conductive mast would be okay?

6. Same antenna but mounted at the rear of the boom.