After finishing ninth in last season constructors' championship, only the second time since 2012 the team has slumped to such a position, Tost was fully expecting a resurgence this year.
The result has left Tost frustrated with his engineering team.
“We have to do a lot of things to make the car faster, especially on the aerodynamics side,” assessed Tost. “There are different programmes going on.
“The engineers are telling me that we are making some good progress, but I don't trust them anymore. I just want to see the lap time because this is the only thing that counts.”
Asked if he was serious with regard to his comment about the engineers, Tost replied: “In the winter months they told me the car is fantastic, we've made big progress.
“Then we come to Bahrain and we are nowhere. What should I say?”
Tost details car faults
According to the 67-year-old Austrian, the problems with the AT04 are numerous. Explaining Tost said: “(There is) Not enough downforce, the car is unstable under braking, therefore overheating the rear tyres, washing out at the apex, bad traction. Everything you need to do a good lap time.”
Tost feels the characteristics of the Jeddah Corniche Circuit should suit a car he has stated will have upgrades throughout the year.
“The question is now, do we go in the right direction?” queried Tost.
“As I mentioned before, during the winter months, we saw that, at least on paper, on a computer, we made big progress in comparison to last year's car.
“But all these figures nowadays, as I mentioned before, I don't trust them anymore.
“I want to see now, with the next steps, that we go in the right direction, that we can improve the performance of the car, that we are able to do this.
“This is especially working on the floor, brake ducts, and all the other aerodynamic parts.
“With all the knowledge we have after the Bahrain test and after the Bahrain race, the engineers should be in a position to sort it out and to come up with new parts which improve the performance of the car.”