I really think its a case of whatever visualisation tool works the best for you , if it helps you to do the technique correctly it is useful.
One of the objectives of the exercise is to teach you to have a constant flow of forward force.
The problem most people have is not with the going out bit , but the coming back bit.
It can be a hard concept to wrap your head around , that is to have forward force on , even when your arm is physically moving backwards , but that is exactly what we must do.
We were taught to drive the movement forward from the elbow , bring it back from the elbow.
In the retraction phase we are still imagining the elbow going forward , intellectually we know the arm is going back , but mentally we are still trying to project it forward.
We are creating a habit and using our brain to try and trick our muscles into believing that they are always in the same state whether they are moving forward or back , ie that they will be relaxed , with some resistance against incoming pressure and ready to spring forward when there is no counterforce to hold them back.
When I practice the form I try to imagine there is a bit of resistance to my elbow movement , and when I train with a partner I imagine the exact opposite , that there is no resistance , the person is not there I am just doing a movement from the form.
It should not be done super slow or too fast , doing either means that you are consciously controlling the speed of your arm using muscle instead of freeing the mind to do its own thing.
Just try to relax and let your mind mind move your arm forward and back , on the going forward phase stop when you get to the angle where you start to feel a bit of slight tension from other muscles like your bicep , this will be very close to being your optimum or ultimate angle.
You have to really relax and concentrate hard to feel this , its a feeling of OK other muscles are just about to engage now I've reached the proper angle time to start moving the elbow back.
