Very interesting. I appreciate that you have exposed more of your listening sensations - that give more objective information, letting to propose more accurately what might took place. In regard to what you say it might not be the “phase clicking” but rather a mild decompression of the upper range S2.
The S2 crossed at 3200Hz at 6dB and pushing in a 400Hz horn 1000hz of air does reaches at it’s bottom the region where a very slight touch of the “Horn Boom” takes place. It is a mild form of honk, very modest and very much not detectable when the channel is supplemented with sub 1000Hz channel. It is possible that moving the crossover point from 3200Hz to 4800Hz you further up removed the S2 from the Horn Boom region. (The Horn Boom is always accompany with compression)
I did experimented with it and not detect that moving up the crossover point was a benefit. However, when I did those experiments (2001-2002) I did not use yet use a Fundamental Channel. So, during that time I was merging the S2 driver with my upperbass horn’ upper knee, which had too heavy cone to care 2000Hz. The lower friqency S2 driver should be way more interesting contestant….
Presumably you discovered an effect that worth to imitate or at least to try. Do you have the vertical image shift slightly up when you change your crossover point higher? Anyhow, let see what will be your further finding or perhaps the final findings. However, there are few things that would strongly encourage you to check before make up your mind, all of them are related to the S2 driver in 400Hz horn
1) Make sure that your cone is properly center in a gap. It is very important as misaligned cone will do compression at bottom end2) Make sure that the driver’s center are absolutely in the center of the horn and absolutely parallel to the horn’s axis. That is also very important with MF driver. If the driver does not sit in a perfect optical center of the horn then it will have very sever anomalies, particularly when the horn is towed in or out. With the spherical, low throat horns, as we have, it is very simple to misalign the center of the driver for a few fractions of mm.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche