Some of it depends on what you expect to carry.

I always felt that my carry percentage went up on tougher conditions. My reasoning is that in order to get to the pocket you have to throw a better quality of shot so when you get to the pocket the carry is good.

Think of how high your carry percentage is on shots that when you let go of the ball you just know it is going to strike.

Far too many bowlers complain today about carry on shots that without the help of the lane or ball would have completely missed the pocket. How many times have you seen someone miss way out (2 or more boards) and the ball comes back and leaves a corner pin (generally the ball is DOA at the pocket) and they flip the pin off or kick the rack? They should have been looking at shooting a spare with 3 or 4 pins standing instead they have a single pin.

An individual’s carry percentage will vary depending on how their style and the equipment matches up to the conditions.

Lane construction and oiling patterns can and will effect your roll pattern.  

If you can’t get the angle and the ball isn’t into a heavy roll as it enters the pocket you are going to leave a lot of flat corner pins.

If your ball is burning up its energy early then you’ll have carry problems.

You have to use either changes in you release or equipment to get the proper shot going to maximize your carry.