Not so much the size of the divorced section, more so the wastegate itself not flowing enough, as far as mods to reduce boost creep, its really a case of more mods increasing the chances of boost creep, the more efficiently the system flows, the more likely you will creep. You may not creep at all with the downpipe alone on the system, but throw on an intake, TIP & IC and you open the pre turbo breathing up substantially, allowing better airflow through your motor.
But even if you are fully bolted and creep is still causing issues, usually a very small restriction in the exhaust can be enough to stop it, a second cat would be barely noticeable power wise, but might be enough to prevent creep. Having said this not every car with a divorced DP experiences creep either.
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