Your numbers look pretty good to me!
When using the “select power source” screen in Zwift I can see directly how my re-calibrated bike compares to the power meter pedals, as it shows wattage from both sources at the same time. Similar to you- I notice that Nautilus output matches up pretty closely with the power meter at mid-range levels, but then starts to get inflated at higher levels.
I think we’ve probably reached the limits of what can be achieved with the hard-coded Nautilus power output algorithm. I suspect that any more tinkering to get my higher resistance levels in line would throw my lower and mid range levels off. Plus, like you say, we’re limited to three kicks at the can for calibration, and I’ve already used two!