Zero
I would not bother with doing the recalc as section 21 is far from precise - in fact it is quite ambiguous.
This lack of precision means basically that the quantum covers
everything - on that basis, it's not far off the equivalent aggregated hourly rate of a casual check out operator at an Aldi supermarket.
Of course even more scary is that the combined agreement concept as you would need to make sure you lobby the CC for their support in respect of subsequent agrements -
It would be far from comforting to think your future relies largely on the votes of starry eyed 20 year old Y gens whose perspective of IR & workplace agreements does not extend beyond whether paparazzi should be allowed to take photos of p*ssed celebs.