As I understand it, the incretin effect causes high insulin when fat/carbs are combined e.g. see the 'Fat and Carbs: A Deadly Duo' section in this edition of Dr Eades Arrow:
https://arrow.proteinpower.com/p/the-arrow-148
There's also been some info in later editions.

On a different thread, JEY100 posted that she was eating 30-40% fat and 20-30% carb which could possibly be in the incretin zone.

My open question is, at what level of fat/carbs is this effect a problem?

(I eat approx 60g carb a day and skip breakfast so I'm starting to think how to separate my meals in to Carb/LF/Protein and LCHF/Protein).