Data Cell Conditional Input using UD3 Constraint

Hi,

I'm trying to block input to UD3 None (for example) using the Cube setting in Data Cell Conditional Input,  but only for accounts that have a certain UD3 Constraint. Basically, I had to add None into the constraint for some rule logic,  but I don't want anyone to be able to enter data there by mistake.

I normally test the Member Filters of blocking rule by just putting the Filter into a Quick View, but I am struggling with this one.  This is what I have:

A#PL.Base.Where(UD3Constraint = MyUD3Constraint_1)

But that does not work.  I think the issue is that the UD3 Constraint can vary by Cube, rather than being a strictly defined property of the member.  Not sure if it's possible to define the Cube in the Where clause?

Any ideas welcome!