Thanks for the comments on the previous version.
In response I abandoned any attempt to reference the photograph I shot on the same day as this painting was first sketched out. I kept changes to a minimum: dropping the skyline to give more explanation to the background coastal hills, smoothing out some texture in the bottom left corner to link better the two halves of the image, scouring back some of the intense white of the nearest sea to reveal colours beneath and selectively glazing the foreground in acrylic to give more shape to the overgrown rock surface and reduce the brightness of the whites.
I now call this a finished piece.