Over the years I have had several vertical antenna setups, they were mono band antennas so the rule of thumb was to cut the ground radials 1/4 wavelength to the center of the operating area.
I began using a Zero Five 43′ multiband vertical 10-80 meters. The effective amount of radials is 32 per band for 7 bands is over 200 radials?
In a recent article I read on the matter length is also irrelevant if the radials are above ground with snow cover or in the ground.
So far the approach I have taken is to make 32 radials 43′ in length the same as the antenna itself.
If anyone has experience with this I look forward to hearing from you.