This completely works. When my stock rear turbo died and I was low on cash so I decided to just replace with another stock turbo. Whilst everything was apart I opened up both the manifold, and the turbo slightly, and once it was back on the road, I was hitting full boost almost 1000rpm earlier. Although it is true about faster air flow when there is a thinner section of pipework ( a venturi) for a turbo to spool well, it requires a greater volume of air to pass by the exhaust wheel. The bigger the path for the air, the better the flow, and the earlier the boost comes on.
Having said that, it would have been a good idea to either block the exhaust side of the turbo from any shavings, or take it apart and blow the shavings out before refitting to the car. After 2 months of having the car on the road, the rear turbo let go again and was found to have shavings blocking the oil return to the engine.... oops
GT-SS going in now though, I might be more careful when matching these turbos to the manifold