So if we are looking at an aircraft with a ducted propeller (or a high bypass turbofan engine), does it matter how long the duct is? As an extreme example, would having a duct that extends 100 feet behind the prop give any added thrust (let's ignore drag/weight effects of the 100 foot duct)? Because from my understanding, thrust is applied directly at the propeller, so it shouldn't matter how long the duct is just as long as it prevents tip vortex effects.

So as a follow up, why do most high bypass turbofan engines have their bypass duct extend back to where the engine core ends?