Actually, you won't push the cart to far down using a paperclip. Inside the mouthpiece, there is a plastic piece that sticks up from the bottom, to stop the cart in just the correct position. This keeps the wick at the proper depth.Using the paperclip method (either end), I found that it was possible (even likely) to push the cart too far down into the mouthpiece.
Using the stopper to push the cart in does work, but sometimes they are a pita to push in all the way. Besides, they are not always handy. For example if you are topping off, you probably don't have a stopper handy, but you do have a paperclip.Use the plastic cart stopper.
This is always to hand and places the inner cart perfectly in the mouthpiece.