I tried the gravel tray at many different heights until I was happy. This is the position I have decided on. It is sitting 19mm-3/4" higher in front of the grille than before, but still leaving more distance from the bottom of the slots to tray.
Bumper back on to finally see if it was worth it or not. The distance from the slots to the top of the tray is now half that of slots to the top of the grille. This is the same proportions as the stock 48 flat nose grille which is different to the 58 pointy nose grille.
Ok, just put together a before and after. About 20 shots it took to get it as close as I could, even brought the dog in! So left the overall height of the grille the same, but shortened the slots by 50mm-2". Then raised the stone tray 19mm-3/4". Also the grille mesh has been added which helps more in the flesh than it does in these photos. I think it doesn't need the horizontal grilles bars to be added as well anymore.