For a 1200, the offset muffler allows you to put the muffler in the correct space, for clearance over the rear axle, which is important when you are using bigger diameter tube.

On my turbo CA18, I run a 3 inch system with a cat convertor and a 14 x 10 x 5 inch straight through muffler at the rear like a 510 (I have coilover rear). That's not too loud believe it or not. But turbos really quieten down a car at traffic speed. It's over 5000rpm that they sound like a screaming banshee.

My old CA18DE had a 2.25 system with hotdog resonator (non-turbo cars really need it), and a largish rear muffler, and it sounded great.