Alonso finished in that position in Hungary last weekend, a place ahead of team-mate Lance Stroll.
The Spaniard was as high as seventh on the first lap, but he lost out to Sergio Perez and George Russell, both of whom were coming through the field after poor qualifying sessions.
Alonso, who logged six podium finishes in the first eight races of 2023, has accepted that Aston has now slipped down the order, with McLaren, Mercedes and Ferrari consistently ahead in the pack that is chasing Red Bull.
"Yeah, I think so," he said when asked if the Hungarian result was the best he could have achieved.
"I think we weren't quick enough to challenge anyone in front, and we didn't have any threats behind. So three points, ninth and 10th, maximum today.
"I think the last two races we are struggling a little bit. I think in Silverstone the safety car helped us in a way to finish seventh, which was a little bit better than our pace.
"In Silverstone and today, ninth probably is our pace. So yeah, behind the Mercedes, Red Bull, Ferrari and McLaren, which is more or less what we saw in qualifying, and what we saw in the race."
Alonso admitted that he was surprised that the pecking order was so consistent over two very different tracks.
"Yeah, a little bit," he said. "I think in Silverstone we did expect to struggle a little bit, but in Budapest we thought to be a little bit stronger. It was not the case. So we try to analyse and get back strong in Spa next week.
"We need to see many things, it's up to us to understand a little bit better what is the car doing now compared to the beginning of the season, how many upgrades we brought compared to our main competitors, and then understanding the new tyres the best.
"They're the same for everybody, so we just need to do a better job."
Asked if Aston was simply losing out in the development race, Alonso said the true situation wasn't clear.
"Difficult to know," he said. "I mean, every race we would love to understand, and we have many questions, but we never know exactly what is the cause of it.
"In Austria Hulkenberg and the Haas, they were fourth in qualifying, so we were all surprised. In Silverstone Williams was very fast, we were all surprised. Here Alfa Romeo was very fast, we were all surprised.
"But then in the race, normally everything balanced out and the big teams finish in front. And yeah, we are just in the back end of those top teams. So we need to get back to the front end of that group.
"We always try to bring things as everybody does. So it's not that everyone will just finish the development and wait until next year. We will all try to bring stuff.
"Some of that stuff works better than expected sometimes, some works worse than expected, and hopefully the next step on our side is a good one."
