I would try for the WG very early in the morning, such as 7 o'clock, or whatever time the sun illuminates the bay after having risen above the height of the spit. The water is more likely to be calm at that time. Observe the grebe for a while and see if and when it passes through the bay's isthmus (mouth of the bay). While hardly what one could call a narrow isthmus at CSSP, and therefore perhaps not the ideal configuration for 'romancing the isthmus' it does improve your chances of getting closer to make your grebence. I would walk to the end of the western spit and climb down to the shingle. Put down my mat (or a blanket) on the shingle and then hit the deck. With your 600mm braced on a small bag of inspiration, inflatable or otherwise, you could wait for the right moment. Heck, you can even grab a few zzz's while you wait. Some RN grebe might traverse the gap while you're waiting for the big bird. Just be prepared for someone to come up behind and shout down "whatcha doin there?" Some people just can't stand it when you are acting serious and putting an effort into getting a better photo.
