Sorry for the late reply, been on the road. I think the "V" shaped detection pattern arose because it was an easy way to verbally describe the pattern. The real pattern looks a bit more like one of the Coneheads from SNL. Here is the V pattern compared to a more realistic pattern:



I measured that pattern many years ago and can't remember what detector I used but it would have been a concentric. Also, it bulges out around the edges of the coil, which is not shown. Although a V pattern isn't a totally unfair approximation it does underestimate overlap efficiency. Here is a 50% overlap of a realistic field:



This creates a full ground coverage at 75% of max depth whereas a V pattern suggests you will only get 50% of max depth. So even with a 50% overlap you will often miss the deepest targets; in fact, below that 75% full-coverage depth you will, on average, miss about half the targets. That's why places are never completely hunted out.

Different coils will have slightly different detection patterns, especially DD. They tend to have a narrower pattern side-to-side but the front-to-back pattern is very similar to a concentric do the overlap requirement is about the same.