That looks like about a 5db peak at 9kHz.
A bit bigger on the stock drivers. It does not intrude much being that high up. The Alpair 5.2 is probably smooth up there but wasn’t on the radar when we started these. A wide variaety of 3” drivers could be loaded into that TL including the LGK, and not much change needed to accomodate larger drivers in the Alpair6.2/7.3 class.
The woofers go up to 5k or so on-axis. I had misgivings about the high XO when i 1st got the design, but in practise it works well. Edged out by FHXL, but a much smaller footprint. Bipolar “viewed” on edge has perfect bafflestep fill-in, issues near the XO will be dependent on the off-axis.
The fellow who did the XOs is a measurement based fanatic, these were measured in a big space, with them 20+ ft in the air. That the measured responses after XO were very close to the sim is an indication of how well he did.