I'm not talking about driving straight down, but rather pushing forward more then normal (to get them to push forward more then normal), and then pulling down. Basicly, tricking your opponent into commiting force against nothing, and re-directing that force.
Okay , I understand what you are saying now but what I said earlier about the skill of the person still applies . You may get away with it against a novice .
But against an experienced practitioner he will use just enough forward force to counter your force and no more. Your force would also be uneven , a rise in pressure on the Fook sau side without a corresponding rise in pressure on the Tan sau side would be detected and taken advantage of straight away.
In our lineage a typical response on feeling an increase in pressure like that from the Fook sau would be to pivot and go into what we call a reverse Tan sau.
The effect of this is because you have committed yourself by using excessive force you will find your Fook sau sliding down the outside of his reverse Tan sau , as he pivots you off to the side and opens you right up , and then pivots back into you and strikes.
I've had the opportunity to do Chi sau with quite a few skillful people over the years , and the best strategy is not to give them anything to work with mate.
Just make sure your angles are perfect , both wrists on the centreline and projecting force to the centreline from your elbows, don't lean , just use enough forward force to maintain your angles , and stay relaxed.
Perfect rolling is your best defence against attacks , and trapping etc.
You give them anything that is not directly focussed at the centreline or uneven in force and they will use it against you . One analogy you can think of with Chi sau is that of a big inflatable leather ball that is rotating at high speed out in front of you .
You try to strike the rotating sphere , because its inflatable it absorbs a tiny bit of your force and then bounces back , but because of the rotation of the ball most of your force is spun off to the side and redirected .
The more force you use and the more committed you are the more you find yourself thrown off to the side of this rapidly spinning ball.
Think of your arms in Chi sau as this sphere , but unlike the spinning sphere our arms can rotate in multiple directions to redirect any force that makes contact with our "Sphere".