I tried on H180 shells (since its the same generic plastic covers from standard 15.4mm drivers) and it's not the best for comfort. The best plastic covers are the ones with metal covers, the best match (from my collection) for the H180 shells is the ones used in 130 ohm beryllium, they are even thinner than the ones in 32ohm PET drivers. This way you can almost achieve the magical fit of the H180 with their original plastic covers. Currently experimenting some white extreme thin cotton tuning foams in the shells (instead of the standard/common grey shoe tuning foams) and it looks like it brings a bit more better soundstage and tame very slightly bass impact, which is perfect for the 32 ohm PET drivers (as they have a lot of bass already). Coupled with some high quality silver plated cable and extreme thin foams (like the ones in VEclan), I really believe it's one of the best earbuds I listened to date for now.