"how much distance do you need to the horns to get a coherent sound?"

I listen maybe 12 ft from the horn mouths. Pretty close.

"is nearfield listening enjoyable?"

Yep, but I don't know how much closer I would want to get.

how big is your sweetspot? on my system there is a 1-person sweetspot.

I have a two-seater that is in the 'zone' but one side is surely a bit 'sweeter'. Big Tractrix horns are not wide dispersion devices. A bigger room and more distance would help here.

could you send me the plans of your chopped bass horns to get a feeling how big they really are?

I see Wayne has sent you the plans - if you just cut out the back and top panels leaving the horn angle itself you will have it. Very simple, and placed in corners, reasonably compact(!!)

cheers,

Shanko