It's not hard to be off axis on those PT2's. It's a choice. Where will you be? Seated or standing? For me it was somewhat unpredictable as sometimes I sit and hen sometimes I stand. In any case, the PT2 is down 3dB at 30 degrees at 10k and down 8dB at 15k. Anyway, here's a link to a dual PT2, 16NSB array.
http://www.diyaudio.com/forums/attachment.php?s=&postid=368532&stamp=1081565756