Yes, looks like only forward incremental and forever forward is supported by the tool.
I have to say, I manage a few dozens customers and no one is using reverse incremental. ReFS/xfs with forward incremental should be the designing best practice for new implementations today. That could be the reason why the tool doesn‘t offer reverse incremental.
I'm not seeing an option to adjust it to forever forward like the old tool could.
For
forever forward backup copy results you can use the calculation from the
backup job without gfs results. The backup job in the calculator supports forever forward incremental. The required space should be similar.
A note:
If you want to use the move policy with s3 storage, you can‘t use forever forward incremental. The backup chain would never be sealed and older backups can not be moved to s3.
I‘m on your site with the calculator is missing somethings like backup job runs per day, backup job type and so. But most of the data can be calculated from the existing results.