Upgrade/Downgrade shows product that shouldn't be available

I have a product "Z" (recurring payment).
I also have a special "downgrade" product that I want to be available only to select people.

To accomplish this, I:

• Created a 'dummy' product called "Eligible for downgrade".
• Set Product Availability for "downgrade" to require an active subscription for "Eligible for downgrade"
• Created an upgrade path from "Z" to "downgrade"
• When I want to offer "downgrade" to someone, I manually add the "Eligible for downgrade" product to their account, lifetime, free.

Works great on the Add/Renew Subscription page - if they have "Eligible for downgrade", "downgrade" is available to them, if not, no "downgrade".

However on the Upgrade/Downgrade popup, "downgrade" appears whether they have "Eligible for downgrade" or not.

Why the different behavior?? Should I instead make the upgrade path from "Eligible for downgrade" to "downgrade"?

One additional piece of information - both "Z" and "downgrade" are in the same renewal group. I need that because I have and upgrade path that goes the opposite way - "downgrade" to "Z". Right? They'd need to be in the same renewal group for the upgrade to prorate properly?

The upgrade path for "downgrade" to "Z" is default price calculation. By design, the upgrade path for "Z" to "downgrade" that I tried was flat price calculation - I want them to have to finish out their "Z" subscription before "downgrade" starts.

Just as a test, I added an upgrade path from "Eligible for downgrade" to "downgrade", and deleted the upgrade path from "Z" to "downgrade". Now, with an active "Eligible for downgrade" subscription, "downgrade" appears on the Add/Renew Subscription page but not on the Upgrade/Downgrade popup. Maybe because "Eligible for downgrade" is free??