The mileage amounts on AS don't differ on one-ways vs. roundtrips, but the carrier-imposed fees on partner award flights can differ based on trip origin.

Delta does something similar and has assymmetric carrier-imposed fees on awards on partner metal depending on origin. For example, UK origin DL business class awards on partner metal currently have a $475 carrier-imposed fee, but if the partner metal on UK-US flight is part of roundtrip booking originating in US, it's only $30 for business class ($10 for economy). There's no carrier-imposed fee on DL partner metal award flights on one-ways from the US. One interesting effect is that although the carrier-imposed fees are small on ex-US roundtrip bookings involving partner metal on return, they do trigger roughly $45 in US international departure/arrival taxes on awards as they are no longer considered "zero fare" award tickets where those taxes get waived.