Howdy,
I don't know how the grip was handled in the past, but for most CAS shooters it's pretty simple. The thumb is laid along side the stock and tang. If you are trying to lever quickly, you learn to NOT wrap the thumb over the top.
I have used the tang sight on a few of my guns and they work very well, but, I've had to fight my creep-up instinct.
Adios,