I do this by using the AI line helper to define custom sidelines for the track that allow the AI to use more or less of the track in some areas. After I define sidelines I load into hotlap mode and use the dev tools to record an ai fast line file. Once I record a fast clean lap that doesn't use too many kerbs and stays mostly on track, I test the AI racing to see where I need to make small edits to improve the side by side racing