Where should the radial wires of a ground-mounted vertical antenna system be placed?
Why A ground-mounted quarter-wave vertical needs a low-loss return path for the antenna's ground currents, and those currents flow in the soil right under the antenna. Laying many radial wires on the surface or a few inches down puts copper in the path of that current so the earth's resistance doesn't eat your RF power. Buried radials are not resonant elements, so their exact length matters less than having lots of them; 16 to 32 or more is typical.
Watch out Radials raised well above ground describe an elevated ground-plane antenna, which is a different design that uses only a few tuned quarter-wave radials rather than a buried ground screen; the question specifies a ground-mounted vertical.
Ground-mounted means ground-level radials: on the dirt or just under it, and the more the better.