The cars run the same cooler, the same exhaust, mine a Power Fc and the other a remapped std ecu. It was 100% a HKS GT-RS, not a Garret, forget what the dyno sheet says. Yes it is a GTS4 but run on a rwd dyno. And two different tuners, mine Racepace and the GTS4 Dr Drift
Yes its running less boost, and perhaps a few degrees less ignition (perhaps, but its possible my tune was the more conservative as it is a track tune so a few degrees short of what you would run on the street). That all said, the general picture is the same.
Also, your plot is a different type of dyno, a different dyno so even more variables to consider. I know my car made 260rwkws on a Dyno Dynamics with the same tune, hell, probably even the same tank of gas So I was down 15kws on the Mainline dyno