Don't worry too much how far the extra light hammer flies. It's more important that you are able to wind faster and keep your balance. That's the goal of training with the underweight implement.

Next time you start winding with the 16#, it will feel slow and you will try to go faster. As long as you're not "arm-winding" to go faster, the hammer will go further.

Wind with your hips, not your arms.