The Woking squad is currently fourth in the championship, 41 points ahead of fifth-place Toro Rosso.
Since the Monaco Grand Prix, the team has scored a sixth-place finish at every race bar Canada - one of only three races so far this year where it has failed to score points.
But despite its improved form, Sainz states that it has not been easy for the team, as it has had some reliability concerns.
"If you add that my first failure came ten laps into the first race of the season, then that's part of the unlucky situation and the penalties that I had to take in Austria," he said. "We managed to recover well with an eighth-place finish.
"It hasn't been an easy, straightforward first half to the season. There has been very little time when we have been the fourth fastest car. We've had to make our way through on race days and it has made the season interesting and particularly good on Sundays.
"But at the same time, I feel like the race team is performing at a very high level, with strategy and preparation. I'm performing well on Sundays and so in the end, we keep bringing in points, that's the main thing."
The Spanish Grand Prix looks set to stay on the F1 calendar next year, with a one-year extension rumoured to be the deal in place.
Sainz says that it is "incredibly important" on a personal level for the race to stay on the schedule, as it is his home event.
"For me, it's incredibly important if it manages to stay," Sainz said. "The rumour that I have heard is the same, that it is a one-year extension, but nothing confirmed beyond that.
"What I really expect and hope is that this one-year extension allows for a longer deal, if it happens, if the rumour is true. But at the moment it is only rumours."