Cassidy claimed pole position in both New York City races, winning Saturday's race after it was red-flagged amid a burst of torrential rain, as he aquaplaned off the road and into the wall at Turn 6.
He was followed into the barrier by both Lucas di Grassi and Stoffel Vandoorne, prompting the termination of the race.
But pole on the following day was taken from Cassidy after being handed a 30-place grid penalty for race two, after requiring a new battery as his car was effectively rebuilt from scratch.
After two weeks to reflect, Cassidy explained that there were lots of positives to carry forward into London's double-header, and that his speed showed that he would have been in contention for more success on the Sunday.
"I'm 100% just looking at the positives," Cassidy explained. "Because the rules that are rules, what happened, and it's something completely outside of my control or my influence.
"So there's no point dwelling on that. I need to look at the things that I can control and doing the best with that. And I think even in the race, I still did.
"I still had things to learn in the race and to push on. And I think yeah, the speed shows that it could have been a very successful race for us.
"But just kind of take that positivity to this weekend now and the rest of the championship and especially building up my group [of mechanics] for next year, really."
Cassidy's pace in the second race at the Brooklyn circuit had been largely in the same ballpark as the leaders, but his race was immediately ruined by the additional drivethrough penalty he had to take - as the full 30-place penalty could not be served.
But the Kiwi says that getting in the right groove in New York with regards to set-up was key to his strong weekend, and feels the Envision team has done its homework for London in order to continue that good form.
"Depending on the nature of the circuit and how our car works, let's see how competitive we are. We hope to be strong. We've done our homework to be strong. But you never know until crunch time.
"However, it's more I want to keep working on limiting mistakes from all sides - not really just from the driving side, but also procedural set-up, systems.
"[We want to] have all that working, like we did in New York, we nailed that a lot more and that makes my job easier.
"So that's going to be the focus on these races. And then I'm sure if that side's there, we're in the points anyway."
