What is a hill?

What parameters does Garmin use to decide what constitutes a "hill" and activates ClimbPro?  Grade, distance, or some combination?  I recently did a multi-day ride with a friend who was using a Wahoo Roam and while we both downloaded the same GPS file there was a substantial difference in the number of "hills" each device recognized.  I believe one day he had 23 and I had 8.  Somewhere in the middle would be nice.  Are the parameters user adjustable?