I've seen an 18' sea kayak on a Smart Car, so your situation is hardly extreme. I've found the greatest hazard with long overhangs of boat vs car is that you as the driver are apt to hit things fore and aft with the boat. This is another incentive to ALWAYS use bow and stern lines tied to the bumpers or sub-bumper structures. Not only is it insurance against having the boat windmill off the car (damaging itself and anyone around you in traffic) but the visual of the lines reminds you where the end points are AND gives you a constant monitoring of the boat's position on the car.
Fastening bow and stern lines takes only seconds, especially when using self-ratcheting ropes. I don't know why so many people avoid using them. I always do, no matter what my travel distance and speed will be.
Heel and Pegpads™
Bent Shaft Canoe Paddles
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