To answer my own question:
This seems to be dependent on the tool used as sflow collector.
PRTG does not seem able to differentiate ingress or egress.
InMon sFlowTrend (https://inmon.com/products/sFlowTrend.php) however is able to differentiate switch, port and in- vs egress without any additional config. As a downside, it requires java and seriously needs a UI update.