I'd been to the Blue Mountains several times looking for this species and H. penelope, without any success. Finally I found both of them in an area of woodland close to Blackheath. The specimens of H. paradelpha were mostly flying close to the ground on the edges of woodland, next to more open areas.
In early February 2009 I went to Jenolan, and there were literally thousands of these butterflies on the wing. I have never seen so many specimens of one butterfly in the same area; it was hard to concentrate, as there were so many of them. It was also hard to get photos of them. Heteronymphas tend to be hard to approach when it's hot and sunny - it's often easier when there's fairly heavy cloud with the odd sunny break. This particular day was sunny and VERY hot, so the butterflies were very frisky, plus they kept on disturbing each other. And finally, they generally jumped when the flash went off, which spoiled most of the shots I took, but I had no choice but to use the flash becase they settled in the deepest shade they could find.

Sightings
Blackheath, Blue Mountains - March 2006, January 2009.
Hampton - February 2008
Jenolan - February 2009
Wentworth Falls - February 2009, February 2011
Lawson - March 2021