To my experience, freqs above 16khz always become smoother, even if they are tilted up. 20khz freq, which is the highest audible one is ultra smooth, no matter the tweeter material. I even have found that a tilt in that end of the spectrum could result in a smoother and airier treble perception.
The hot freqs go from 2 khz to 16 khz, which are mostly related to the tweeter design and resonance, regardless of the voicing. That’s why in most of the cases a hard dome tweeter sounds hot in comparison to a soft dome, which sounds smoother. It is not a straightforward rule, but it applies in most of the cases.
What most people call treble are freqs between 5khz to 12khz. If a speaker is tilted up there, everyone will describe it as a tilted treble speaker, even if it completely rolls off above 12khz.