I really like this question..... and I admit to still being baffled....
A Mirage 2000, a Rafale or a Mirage F1 is only about 15m (50ft) long.
Yet the booms we get locally (see above re returns from exercises over the Med), are still the same double boom - "whah-boom" (N-wave).
Of course, when it comes to judging the exact duration of a sonic boom, things get very subjective.... I wouldn't trust my own judgment, since it's as much based on the rattling of the window/door as the actual sound.
CliveL, are there any documented records of the trials in "Boom Alley" we could use to settle some of the issue?
CJ