Lars mentioned that he had for now opted for an axisymmetric device due to its simplicity, for the demonstrator, but would be looking into elliptical geometries in the future.
Those offer more freedom with baffle placement and hence sound power optimization, and can be used to tweak the tilt of the combined DI, when a horizontal constant and a vertical pseudo-exponential profile are combined.
Re VHF dispersion, the simulation results without a phase plug look very encouraging. The 130 degree horizontal pattern (65 degree) of the Jbl M2 is commonly describe to present a big image. This is reached already in the simulation results. Also, the phase plug that Purifi relies on for an even wider top octave creates a very strong loading of the top octave. This might lead to rising frequency response of the LW angles.