I am in the process of creating actions to create masks that will use the zone system instead of the 'regular' mask creating actions (That I have already hacked to death - See long ago postings).

I have basically discarded the mask* Level** option for being too wide and basically crap (in my opinion). I have selected the curve*** option instead. The mask then is much more pointed and can be made to adjust the output more precisely than when using Level.

I get the feeling that I am digging my own grave here...
check out Jimmy McIntyre, he has created Rya Pro that does this but he also shows you how to do it manually. You could create your own action by expanding on that.
Anyway, I am unable to find the range of luminosity needed for each zone. I have tried three different charts (downloaded from internet) and found three different value when probing them for value... If you have those, can you post them?

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* Alt-Click To enter the mask edit mode
** Ctrl-L Level adjustment undo-able, this is not a layer****
*** Ctrl-M Curve adjustment undo-able, this is not a layer
**** This is undo-able only by using Ctrl-Z after the edit. If you do something else after that, CRTl-Z becomes a problem, better start the mask edit from scratch...

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Here is how to try:
Open any image, it does not matter.
Click on channel tab
Ctrl-Click on RGB channel
Click on mask icon
Name this 'Base' (You will need it to compare the masks created)
Remove the selection (Ctrl-D)
Duplicate the Base mask three times
Name:
Mid-range - Narrow
Mid-range - Wide
Mid-range - X-Wide

Click on Mid-range - Narrow
Ctrl-m to enter the Curve option
On the lower point to the left enter the values 0/111
Click anywhere to create a middle point, enter the values 127/127
On the upper point on the right enter the values 0/143
This create the most restrictive Zone 5, the range is only 32 and the output 50% (127)
Click OK
Note that this mask change is permanent and you cannot adjust afterward.

Click on Mid-range - Wide
Ctrl-m to enter the Curve option
On the lower point to the left enter the values 0/95
Click anywhere to create a middle point, enter the values 159/127
On the upper point on the right enter the values 0/159
This create a restrictive Zone 5, the range is 64 and the output 62% (159)
Click OK

Click on Mid-range - X-Wide
Ctrl-m to enter the Curve option
On the lower point to the left enter the values 0/63
Click anywhere to create a middle point, enter the values 255/127
On the upper point on the right enter the values 255/191
This create a restrictive Zone 5, the range is 64 and the output 100% (255)
Click OK

You have three very different Mid range Masks

You should experiment on your own with this stuff as it will allow you to create incredibly pointed masks.

The interest in using this that you not have to mess with inverting the mask in order to adjust the dark. Ctrl-Click on the channel mask to select it.
Click on RGB (if you have not done so already)
Click on adjustment layer, the mask is created, as usual when using a selection to create a layer.