Wader help please(Curlew Sandpiper? Sydney)

Hi all - I can normally puzzle out my birds if I get a photo or two, but I'm an absolute novice on waders, and find them very difficult indeed. Was at Landing Lights reserve today and was photographing a group of Sharp-tailed Sandpipers (at least, I think they are sharpies :-) ) and found a different bird in their midst. 

Similar size, longer black beak,pretty undistinguished, but from the front there are red markings on the chest, looks like the remnants of breeding colours perhaps? Which led me to Curlew Sandpiper, similar size, right size & colour beak & legs, white eyebrow, non-breeding feathers look right, and red chest when breeding. But could completely be barking up the wrong tree, and not confident at all in my pick, so would love to get some help from someone who knows their shorebirds. 

Thanks :-) 

First couple of pics show the bird in question, the 3rd pic shows it with a group of sharpies, both for size context as well as showing the frontal markings