200 Exhaust Spacer

[noobi]

I remember reading that adding a 10mm spacer on the exhaust works in a similar way as the pv cover to boost bottom end.
I understand what it is and how it works, but where does it fit?
Over the exhaust flange on the engine and under the pipe flange?
If anyone who has done this mod has a photo I can look at, that would be good

thanks