63 Flavia Coupe exhaust

[BlueKSO]

Whilst tinkering around under the rear of my 63 Coupe the other day, I noticed an anomaly with the rear of the exhaust system which didn’t seem quite right.  The main single pipe from the front is about 2in dia.  It goes into the first silencer, which is a transverse box.  It exits the box with a dia of about 1 1/2in, continues into the second silencer, in line and exits that box also with the smaller dia.
 Now I’m not up to speed on tuning exhausts, but it does seem a bit odd that the exhaust pipe should actually decrease in diameter. My thinking being it should at least be the same diameter.

Looks like a standard system, but is it?

Anybody like to shine a light on this?

Cheers,  Peter

Ps:  I don’t expect everyone to go scrabbling around under their cars for an answer.