I wish I could find the scientific study but it was a study about where energy comes from during exercise. Like many exercise studies, it used cyclists on a cycling ergometer. The cyclists exercised at different intensity levels and then measurements were taken. At rest all energy needs were met via free fatty acids and blood glucose. As aerobic intensity increased glycogen and fat usage (I can't remember the exact type of fat but whatever muscular fat is called) both increased as muscles were now having to work. Both kept increasing until a certain point (it was 65% but I can't remember 65% of what - V02 max, lactate threshold, max heart rate, FTP - but it was at a moderate intensity) and after that fat usage actually decreased and carbohydrate usage shot up like a rocket.
So if you were actually interested in burning lots of fat it seems the best way to do it would be to ride at a low-moderate pace as well as get that low-moderate pace as high as possible by, at times, actually consuming carbohydrates and working hard to increase your fitness.