S...can't say this for certain, but if I were a betting man, I'd bet that it's not a brake fluid issue, but that you are running stock brake pads and calipers. The pads that come on our bikes are some of the cheapest, low bid products HD can find. Add to that the calipers, and when the pads get heated up, along with your standard calipers and rotors, your brakes suddenly become even less effective.
If you want to see more wheel on front, go to an 18"...Metz makes a 140/70x18 front that is rated very close to stock load ratings....within 40lbs. Overall diameter of wheel/tire is within 1/2" of your stock tire/wheel. That, and more open, floating rotors will let you see more wheel.
JMO