idml import is getting better!
One thing I noticed was the absence of the "gradient feather" effect.
I could not find a corresponded effect in Publishers fx panel, so I assume this is the reason it is omitted.
So if affinity does not want to do this filter at all (which would be sad), at least for IDML import it could be automatically "translated" by adding a transparency gradient which exists in Pubs tools. This is now a manual and painful workaround for big docs...