One problem with depth of field with a dash cam is the need for low light performance, night shots.
A large aperture (low number) lens like a F1.2 to f1.6 is the worst for depth of field.
Vari-zooms might have a relatively large aperture at the wide setting, but at the tele setting is gets smaller (larger number).
Picture a restriction in the light path that is f1.2 at the wide setting, say 6mm. The iris is theoretically 5mm.
Zoom in to 22mm tele. To keep the f1.2 aperture at 22mm the iris would have to be 18mm in diameter.
While it is possible to design a zoom lens with constant aperture, the ones we use for dash/action cameras probably aren't.
That means the tele depth of field is improved by the iris restricting the light coming in.
One way to verify this it to take a picture and look at a histogram of the image and shutter speed at wide and tele settings.
When setting focus on a dashcam, don't try to get objects farther away than the pixel resolution allows.
In other words, why bother trying to get something 1/2 mile away nice and sharp when the pixel resolution doesn't display anything other than shapes anyway.
Focus back until distant objects are just noticeably 'unsharp'.