I always found that NEO 3 pdr is a nearly perfect tweeter excepted the frequency response.
When I studied the construction, I found that this tweeter sufering of diffraction because of the magnets in front of the diaphragm.
So I've design some flexible resin shape to bond on the tweeter surface (on both side)
This shape cancel the diffraction effect of the tweeter housing
It's 3D printing with formlabs flexible resin:
It's far more effective than I though, nearly perfect response (green curve after modification, red before modification)
I will give up the waveguide!