How far the coping sticks out is a matter of preference.
For my quarterpipe I have the coping flush with the transition, then sticking out the top about and inch, there is a good side shot of coping here:
http://www.xtremeskater.com/minirampplans/step2.php. When I have built ramps with Chad from Resiramps (who is much more experienced than me), he always has the coping stick out about a half inch from the transition, so your wheels hit the coping a lot more.
Try to check out a skatepark or find some ramps somewhere to figure out your preference for the coping.