Originally Posted by https://www.asiamiles.com/en/terms-and-conditions/service/flight-award-upgrade-awards.html
1. Members can redeem Mileage Credits for an upgrade
to the next class of travel from the original class of ticket purchased in an eligible fare class
(refer to the Awards Charts page).
Originally Posted by Right under screen cap
- Only fare classes Y, B, H, K and M are eligible for Economy to Business Class Upgrade Awards (for flights without Premium Economy Class only)
Theoretically if there's equipment swap and you can upgrade as such on 2-class flight (which has to be regional business except 33E). I'd consider it an unnecessary complication to add logic to check what plane operates which route and what combination is impossible, which screws things up if forgotten to update some information during seasonal schedule update. I think the above line of rule is clear enough to supplement what's possible or not.