Hey Richard,
We have passed challenges with Prop Firm robots and Petko has also made videos about it. Here you can see one of the videos:
You just need to adjust the settings correctly. But that is not the only thing that will determine if a challenge will be passed or not. It can be the market conditions, the period which you know there are losing and winning periods for the EAs and these are things that you cannot control.
So, what I would say here is just to keep testing the robots, you can also try in demo account and simulate the challenge or in some prop firms, you can have a trial where you can test the robots there as it is like taking a challenge but with no risk at all.
Kind Regards,
Nikos