I was finding the variance in AI from event to event frustrating so this is my current method for the monthly events. I set it to max 8 for practice and tune my car, gives me a laptime goal to know my car is likely competitive. Then I will turn down the difficulty while selecting my grid spot, usually if it says my finish will be 2-4 that is a good level of challenge, usually in the AI 5-7 range depending on what AI lap times it spits back at me. Sometimes my only option start in the middle to battle towards the front but other times its more fun to start towards the front with higher AI and have to defend the position while trying to gain the last few spots. Not perfect but it keeps me from dominating races while also making sure I can be competitive at the front.