Does it matter where you ground a circuit? This man built a 6000V DC power supply (I'm not going to build such a thing.), and he grounded the doubler circuit to the point in-between the capacitors. (You can see he grounded it to the block of the transformer, which is also grounded to the case.) The Organic Chemistry Tutor grounds the circuit at the negative terminal of the second capacitor. Does it make a difference where you reference ground.

6000V DC Power Supply
https://youtu.be/OBQTBgFjFsQ?t=1355

Organic Chemistry Tutor
https://www.youtube.com/watch?v=iDQRB8DOJE4