I think that when garn sau will fail is when the WC practitioner doesn't move forward enough into the kicker. When I've used this in sparring and demos too, it only works for me if my stance is planted where their feet are.
Hense, they kick to head in a round house.
You MUST shoot in with stance and be standing where their kicking leg was before they kicked. Rooted in stance so your not toppled by a heavy leg or strong kick.
flowing from garn sau immediately to tan sau is cruitial too. This keeps your arm from being broken.
If you stop in moving forward with this technique you could very likely get your arm broken or your head knocked off.
Plus, alot of what I consider "good kickers" chamber the kick. I used to be a pretty good TSD kicker, and we did this.
In effect, you chamber your knee and leg into a "ready" position a nano second before you kick, hense chambering the kick. When you kick, you immediately bring your leg back to this position. This makes it harder for someone to grab your kicking leg and re-chambers your leg for another immediate kick, i.e. same leg kick combos.
If they kick and then take the kicking leg to "step" with leaving most if not all of their weight on the front leg, they are vulnerable for sweeps, and a broken knee. This is why you chamber after a kick, to keep from placing the kicking leg down with too much weight on it.
I've not come across alot of people who do this. Garn sau would still work but may be awkward if the leg is pulled back after a kick.
But, as long as your core (body) is touching theirs, and your stance is taking up their stance, it's all good.
Like a baseball bat being swong at you. The more you step into the "handle" or arm of the bat/opponent the less force is in the weapons attack.
The further out away from a good kicker, weapon weilding swing to your head, or even a good boxer, the worst off you are. From that range they have utilization of full power. The more inside you get the better for you even if you get a bit of the knee, or even better, the theigh. It's not going to hurt you. Maybe a little jolt, but with good abduction and stance you won't get knocked over.
A kickers worst nightmare:
Everytime they kick they get kicked in the very leg their kicking with. ouch!
This can be easy espectially if you learn to read their stance and weight position. If their weight is heavy on the front leg, their going to kick with the back leg. If their weight is heavy ont he back leg their going to kick with the front leg. With a one leg forward stance you CANNOT keep from telegraphing your kick. The weight of the body has to go somewhere, the stance is wide and the kicker has to very visably shift their hips to shift weight from one leg to the other.
They go on the ball of the foot on the front leg and turn that ankle, it's a back spin kick of some kind. Telegraph big time! They show you their butt, kick them in the butt, don't worry about the kicking leg.
Take the kickers space AWAY. Jump in there. They freak out, waste time trying to get away from you to get space to kick. Don't let them have it.
Don't let your opponet have ANYTHING that they want, actually. lol! They want to dance around and have space to kick, take it away, corner them, pressure them.
If they want to get in close and clinch, keep YOUR space while taking theirs.
If a boxer is feigting and trying to bail you dancing around to get you to rush in so they can do their awesome combo move. Don't fall for it. Heel kick them in the leg or stomach. Their footwork is really fast and versitile, stop that footwork! lol! Kick that dancing leg, step on that front foot as they shoot backwards and jab, and cover chainpunching or deflecting. Then stick to them like glue! Chi Sau time! Woot!
Sorry, feeling a little frisky today!
But, I hope some of these strategies help in the general idea of WC/WT application of principles and concepts.
Simple, simple, keep everything simple.
If your WC technique isn't easy then your doing something wrong or trying to hard, anticipating, or thinking too much. Trust me, I speak from experience for I do all those things too.
Play WC/WT, play seriously.