Changing co-op difficulty

Hy guys!

I’m playing horizon 5 at the following difficulty settings…
Expert, anti lock system on, all other driving assists are off… Full damage to the car.

Normally I need about 2 to 5 attempts, to win the race and I’m totally fine with it. I need this challenge.
But then there was the gauntlet… The long dirt race. At about 40% the tyres were gone and I couldn’t steer.

Instead of changing my difficulty settings, I asked a friend for help. But in co-op we discovered a big problem.
The mighty S1 and S2 enemies, were B and C Grade… After a few meters, I was in the lead with a big gap…
I’m really frustrated… I don’t wanna win at this conditions.

Is there a chance to change the difficulty in co-op?
My friend and I had set the difficulty to expert.
He does have some driving assists on ( do we have to set exact the same options? ).

Can you help me?

Best regards