If the ground radials go from 45 degree sloping downward to straight
horizontal, at what point does it become a ground plane and not a dipole?

Roy Lewallen wrote:
The antenna you're describing is a dipole. Half of the dipole is the
upper vertical wire. The lower half is the radials. Changing the length
of one half has the same general effect as changing the other half.

Roy Lewallen, W7EL

David Harmon wrote:
When making the standard VHF-UHF ground plane antenna as illustrated in
all the books, with four ground radials sloped down at a 45 degree
angle, are those radials a tuned length? How much difference would it
make if they were some random length considerably longer than specified?
(as, for example, using the antenna on a different band by merely
changing the center vertical element.)