It's a bit counter-intuitive that for an HF vertical antenna (such as a quarter wave monopole) the best advice is to put as many radials and as close to the proper length as possible.
The typical VHF/UHF "ground plane" antenna works on basically the same principle: a quarter wave monopole plus an artificial ground plane. But in the case of these builds, usually only four radials are ever used!
Usually the allowable "gap" when converting a theoretical flat surface to a works-in-practice build (e.g. discones and parabolic meshes and such) gets smaller in proportion to the wavelength. Yet here it's just the opposite — for a 160m vertical monopole I'd still want a zillion radials, yet for a 23cm vertical monopole somehow only one every 90º is totally fine?