With the ports plugged, I had plenty of treble by the numbers. But it seemed I didn't by ear.
I'm no golden ear, but I do listen to jazz. Plugged, horns sound a bit less brassy, so maybe it cuts down overtones? I can hear more clear differences between sax and trumpet with the ports open. At least my brain says so.
I can also hear the studio better on Kind of Blue. "Air" as they say, if I am using that term correctly. If you can access the extended version, it has studio outtakes. It's very easy to hear the studio in those, and then you can listen for it on the main tracks.
In the end, after adapting and tweaking, all that matters is which you like more. Options are good!