WIX doesn't even show efficiency (beta ratio) numbers anymore. All they show is that the Nominal efficiency (which is 50% efficiency) is 15 microns.
WIX 57055 Specs:
When they use to show efficiency specs, most standard WIX filters would have a beta of 2/20 = 6/20 which means 50% @ 6 microns and 95% at 20 microns.
If they show Nominal at 15 microns for the 57055, then I don't see how it could maintain an efficiency of 95% @ 20 microns.
If you want a direct answer, you should contact WIX and see if they can give you the efficiency at 20 microns. Don't be surprised if they tell you "
it's proprietary", which is a cop out IMO.