In order for an airbox to work correctly you will need to have any walls surrounding the air filter at lease an inch away from the filter surface other wise it will impead flow.
While your design is great with effort, the added intake length will change the way your bike will run. It will result in maybe a little more bottom end torque but your high end revs will be hurt.
In order for the pipe not to affect the intake track length, yes it has to grow roughly 30 percent for every inch of length.