I do have another shot, will add it, although I don't know if it will exactly help. Also see butterfly sighting http://canberranaturemap.org/Community/Sightings/Details/2458112 for a few more closeups
What are the key features that seperate this from Persicaria decipiens? If my assumption that http://canberranaturemap.org/Community/Sightings/Details/2458191 is Persicaria lapathifolia, I am fairly sure that this is a different species as the overall impression I got was fairly different. Subsequently, I have had a look at the plant net and noted a few things: P. decipiens is meant to be up to 30cm high whereas P. lapathifolia is meant to be 50-180cms. Every plant in this large group of this plant was probably about 20-30cms high.
I have also put in a closeup (or there is a better one in the butterfly sighting), so Michael could you have a look at that? What is the difference you were looking for there?