Great! Indeed, for single select fields you can find smooth solutions.
In multi-dimensional custom field cases, you have to implement in each measure used in the report, that the Page filter should be applied to the issue epic and ignored to the issue itself.
I noticed you already have found a community thread where my colleague shared a calculated measure that would do exactly that: Filtering on Program Increment at Epic Link level - #2 by zane.baranovska
Instead of using [Program Increment] in the formula and report, you would use your custom dimension both in Pages AND in the calculation formula of the measure.
If you already have a report where you struggle with that, you may share it to support@eazybi.com for more detailed assistance. Then share the report definition and a brief description how far did you get and what is still missing.
Best,
ilze / support@eazybi.com