Technical exhaust question.

[muhuha]

Hopefully someone can help with my technical question, i'm putting an extra silencer (12" straight through baffle type) in my exhaust system it's 2.5" which is the same as my current exhaust. my current exhaust system goes Turbo>elbow>downpipe>(then straight exhaust where i could put the silencer)>centre box>(more pipework where i could put the silencer>directly into my backbox.

I'd say the location closer to the engine i would reduce more noise but the location near the backbox would be an easier location.
Can't see the gas flow being effected because the standard exhaust is 1.75" and current is 2.5".

Cheers