Air purging is said to work better on 4mm filters and typically moves one third to two thirds of the remaining liquid. Tests showed that even if some BAC stays behind, most of the peptide still reaches the vial or cart so the concentration difference is small and basically negligible. I ended up using air on 4mm filters and BAC on 13mm ones. So far I've only tried the 4mm size and they worked fine; I'd switch to 13mm only for something like GHK-cu.
I saw test results somewhere on holdback volumes for different 13mm PES filters using both BAC and air flushing after the liquid. While reconstituting I decided to try the air method so I wouldn't need to save extra liquid for flushing. Once the vial and cart were filled I drew a full 3 ml of air, reattached the syringe, and pushed. Roughly half to two thirds of the air went through and released about five or six drops into the vial, but then the plunger locked up and I was afraid of tearing the membrane if I forced it. The vial was vented and the plunger still wouldn't move even after I took the syringe off the filter.