The Walkinshaw Andretti United driver was first of the Blue Oval contingent home in Race 16 at the NTI Townsville 500, the first encounter with the new rear bodywork on the Mustang following a parity review.
However, that was in no small part due to the decision to run the #25 Mobil 1 Optus Mustang on a three-stop strategy, and Mostert said in a post-race television interview that “it feels like we don't really have a rear wing.”
The changes were implemented off the back of a collaboration between Ford homologation team Dick Johnson Racing, Supercars' Motorsport department, and D2H Advanced Technologies, which conducted CFD work.
There was also race track validation, details of which remain something of a secret, although it is thought that Tickford Racing's Cameron Waters had some limited running at a damp Winton before DJR driver Will Davison spent a day cutting laps with various packages at Queensland Raceway.
Asked by Speedcafe if there needed to be more testing, involving more Ford teams and drivers, Mostert laid the blame on Supercars' VCAT process, which was conducted during pre-season homologation.
“I don't know if it's even that [extra testing]; I just think it's about doing stuff properly,” he replied.
“Every other category around the world uses wind tunnels and does homologation processes to the best that they can.
“Still, I don't know any other category that still runs cars up and down a runway to work out what's going on, to be completely honest.
“To be honest, in the previous history of Supercars, it's been pretty good, but as you can see this year, it's been pretty light on the Ford side for sure.”
Mostert said WAU decided on the three-stop strategy “probably about Practice 1” when they became aware of how high degradation might be for the Mustang at the Reid Park Street Circuit, where a tough life for tyres had already been predicted before the weekend.
He said his car balance was better for just changing rear tyres during pit stops.
“My car balance was better with two tyres,” he advised.
“There's definitely a pretty bad balance with the car, the way it is, and for us, when you have a reused front tyre and the [fresh] rears, the balance actually looks after it a little bit nicer.”
Elaborating on his earlier comments on television, the 2021 Supercheap Auto TCR Australia Series title winner even quipped that he had a more effective rear wing on the Audi RS 3 which he drove in that competition.
“To be honest, I've had a TCR car that feels like it has a wing that actually works more than this one,” he responded to Speedcafe questioning.
“The biggest issue for us is the high-speed, just going through [Turn] 6, trying to hang onto the rear of the car through there, all the exit of 8, all the way through the tram tracks, all the way out to 11, the car's a handful.
“Once you really start to hurt the tyre through those corners, even the braking is quite horrendous in the car.
“It's like it gets the speed wobbles under brakes and you're just locking rears the whole way in.
“So, you're so compromised in braking. For me, I feel like I brake at 50 percent everywhere; my calves have never been so happy in this car compared to our old car.
“You don't really know how to attack and even when it comes to qualifying, for us it obviously cleans up a little bit – you've got a real fresh tyre on – but even the threshold just doesn't feel quite there for us.
“There are some guys in the Blue Oval camp doing a fantastic job in qualifying but, for me, it's pretty clear as day in the race that it's pretty much the same outcome for everyone in that.”
Mostert remains the top Ford driver in the championship, sitting fifth at 141 points behind Race 16 winner Will Brown.
Qualifying for Race 17 at the NTI Townsville 500 starts tomorrow at 10:00 local time/AEST.