How do you mean by "requisite input filtering which is usually a PI shaped configuration of C-L-C"
It shouldn’t matter for a test.
How did you come to that conclusion? Was it just a guess. Indeed it does matter, as per mentioned due to variations in silicon, the two ground potentials are different.
A PI topology filter is usually implemented to suppress EMI and in general is a good practice as you will see it in many power supplies. It is a capacitor in parallel, followed by an inductor in series, followed by another capacitor in parallel.
https://en.wikipedia.org/wiki/Capacitor-input_filterYour best bet is to just copy (within reason). Look at supply topologies and how most input stages for power supplies are designed, that should give you a few hints.
What type of regulators are you using? Make sure you do not violate the input and output capacitance stated by the datasheet.
Do you have decoupling for the pre-amps?