Below is a little diagram of my chimney and what I think I need to order. I am a little unclear on how the extend-a-cap kit works and whether it's better to have too much pipe or not enough pipe. Seems unlikely the rigid+flex liner end up exactly flush with the top of the chimney, so do I want the rigid pipe to protrude above the terra cotta tile at the top? Or do I want it to be slightly below? Should I change that last 3' section to a 4' section? Thanks!