I think it's important to keep the palm up shape, to hook incoming punches between the back of your hand and your wrist so you can twist into a grab/fook or sink it down and expose their flank.
What does your wslvt have to say about that?
I would say taan-sau is not a block and that fuk-sau is not a grab.
They aren't shapes for applications.
They are both training tools for developing striking ideas with dual offensive and defensive functions.
The important part is the elbow, as the hand can be a fist or palm as needed.
People look at the hand shapes in the training tools without information, and wonder how they can be used.
This mostly leads to arm-chasing techniques, as the striking concepts are lost.