I understood your goal is to use more Calcium reactor when PH is ok and use more Kalkwasser reactor when your ph is low.
I think using Calcium reactor in on/off mode is not good idea because it's too ON/Off and not enough flexible.
You didn't answer number of time you will test daily the kh?
If it's twice or three times per day, you will stay 12 hours or 8 hours with last measured kh. so your Kh can go two low or two high when you will have a high kh consumption.
It's why GHL propose a calcium reactor mode in the kh director control panel. To act proportionnaly on your nominal value of Ph inside the calcium reactor.
perhaps here, a valid request would be to having the capability of using Calcium reactor mode for kh on one pH probe and acting on another pH probe in KLalkwasser mode. to be able to react on both proportioannaly.

And last remark: as you are using kalkwasser in limewater mode, I suggest you to use it in 100% case of your evaporation compensation to use it at max. And the remaining need of kh of the tank, can be answered with your Calcium reactor in proportional mode.
By this way no need to having any evolution.
And continue to use your electrovalve as security to do not go thru kalkwasser when the pH is too high.