Eccentric Duct Reducers/Justification using Ductwork Fabrication Parts

Hi everyone, can someone offer me some advice please on left/right/top/bottom justification of ductwork/eccentric reducers when using fabrication parts?

I can achieve this using normal ductwork systems, however I cannot find an option when trying to create it using fabrication parts.

I have tried creating the fitting using the normal systems ductwork and then used the 'design to fabrication' feature and the reducer doesn't get created and I get the following error code .........

"Not all parts were converted. Eccentric transitions and taps that have offsets from the center line are unsupported and cannot be converted".

Many thanks!