I know this goes back a bit... I ended up using 8ohm 2226's my first pair of 4pi's which I've been enjoying for a couple of years. I've just built a second pair using my 4ohm drivers and refered back to your post above for the HF attenuation values...
This didn't occur to me before but if the 4ohm is 3db LOUDER than the 8ohm at a given drive voltage, then surely I need to DECREASE the attenuation in the HF crossover circuit, not increase it?? Or am I not thinking correctly?