IMO the reverse hook kick is generaly trained with a target paddle rather that a heavy bag or stationary object so it can travel through the target. This is not to say it can't be done as shown. The text references the "Dual purpose" of the kick. One to kick and the other to hook the opponent who moves in. (Not a fan of the latter and it would seem that requires less of a chamber.) )This is version A with no chamber and no hooking.
Because we've only kicked shields, my ITF school never drilled the hooking version (and the pattern(s) using it aren't trained because we had a mixed group and that pattern was high Dan .
So is chamber optional for the hook version or is it a demand if you compete in forms?