Hi Gary,
The Conditional Logic extension works only for fields in one page. So if you have a settings page, you can set conditions for the fields inside. But you can't set conditions from another settings page. The purpose of the Conditional Logic extension is make a field visible/hidden in real time, and thus, it has to know the fields in the current page.
As the settings page is created by you, you can control how many fields are there and can avoid a super large array of settings. WordPress supports quite well for the length of option value in the database.
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