As a fulltime panoramic photographer I use a huge range of equipement and I think of all the formats I use as panoramic.... I`ve been shooting this morning the glorious autumn colours here in central otago NZ...... I used 180 lens on my Linhof 617 the most often this morning because of the strong directional and intense light at the time...... yesterday I was mainly using a 28mm lens on a 220 film Roundshot, this again was due to the prevailing lighting conditions which was a nice soft but bright light giving very even lighting on 360 degree pans.
I use several roundshot cameras , a 10 inch cirkut and 12x20 as well as the 617 Linhofs and a 150 Noblex. The noblex only has an aspect ratio of 2:1 but is most definitely a panoramic camera.
The range I use goes from a 15mm lens on the 220vr roundshot which gives a negative of approx 50mm x 95mm this gives an image which is 110degrees vertically and 360degrees wide and yet only has an aspect ratio of less than 2:1 but is obviously very panoramic ( panoramic literally means to see all ) yet fails to meet the more than 2.5:1 concept.
The other end of the range for me currently is 1200mm lens on the 12x20 ! not a very wide view at all but the 12x20 format is generally accepted as panoramic.
What I`m trying to say is that you can`t put a formula to it... doesn`t make sense to...!!!