Help Wanted How to change the MipBias of PSB files that got imported with the PSD Importer?

Normally I can change the MipBias of my sprites by changing the MipBias in the internal Debug window. I change it from Standard ("-100") to a value that works for me (generally "-0.5").
I do this with normal sprites to have my sprite appear more "crisp" / "sharper" for a bit longer, when zooming out. Because in my opinion Unity changes to lower MipMaps-Levels just a little too early.

Now that I use the PSD importer to import PSB files, the standard value for the MapBias is "0", and it seems that chancing this value does not have any actual effect on the sprite set.

(More information about MipBias and MipMaps in general: click here)

How can I change the MipBias of my PSB files?
If that is not possible with PSB files, what alternative do I have, so Unity displays higher level of MipMaps for longer, while zooming out?