its mainly leaf width - see Poa labillardierei (Common Tussock Grass, River Tussock Grass) P. sieb "leaves fine and soft, c. 0.5 mm or less in diameter" and usually bluish according to the Poa key at https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Poa So I think these couple of tussocks are P. sieb (There are some bluish P. lab around in horticulture, selected because of the colour I guess.)