I did not notice this when I first updated to 1851, but since then I happened to delete and re-add my V2s.
Now I get the drag-to-resize box, not the previous detection zone grids. It doesn’t matter in my current setup but if you need the grids I would suggest not to delete/re-add your V2s.
I suspect that if you turn off your detection zone it’ll come back as a big box, not grids on iOS.