"On an Indy weekend, the car evolves a lot, the track evolves a lot, it changes a lot," he continued. "When you start the race, at least this year, I didn't know if we made the good choices or not. By the end of the day, the track grips up, sometimes it doesn't. So it moves a lot.
"But I still haven't got the balance that I wish to have. I think I had a good car today, solid, but there was a little bit of understeer. I was able to just push, push, push. But I think it's more to do with the fact that I knew the track a bit more."
Confirmation that he can put in a strong performance once he has the familiarity with a circuit gives Barrichello a major confidence boost for when he looks forward to his likely sophomore year in the IZOD IndyCar Series.
"It's the way forward to come back next year," he agreed. "I think it can be just a better year just for the fact that you have experience on it. I take my notes, my memory and everything.
"I thought that I would get familiar quite easily with things," he admitted. "But it's quite a lot different. Just the driving: some of the tracks are very, very different from Europe. If we had eight races, I said that before, on new tracks, then eight races again on those tracks, I think I would have done much better."
But before he can start reaping the rewards of his increasing knowledge of US venues, there's one more new street course to get to grips with - next weekend in Baltimore.
"I watched [last year's Baltimore] race a couple times already, but it's the first time I go there. I don't know if it's slippery. I don't know how it is. So it's difficult," he admitted. "Just the fact that you know where you're going to brake."
A lack of testing opportunities has certainly been an issue for Rubens in his transitionary year.
"I think the fact there is not a lot of tests on those tracks is tough on a rookie," he said. "You just don't have the practice. If you take the young kid which is very fast and bright, like Newgarden, he has done so many laps on Indy, so he has some knowledge of what to expect.
"For me, it's been quite tough. I'm happy: I'm looking myself, when I go back and review, I gave my very best - but the results were quite poor," he conceded. "I thought we would have been a bit more competitive."
"I didn't think I was going to come here and just all of a sudden win," he added. "I think there are plenty of really good drivers on a series that is very well competitive. It's amazing."