You're trying to fill and pressurize a 1/2'" diameter passage, which feeds all of the oil leaks in the engine and needs to be kept full and under pressure. The pump has to draw oil through whatever plumbing you're using to feed it and accomplish that. Anything you do to relieve the restriction on the inlet side of the pump will help it to do it's job.

As the pump turns it opens an internal space between the rotors that creates a vacuum. The vacuum creates a suction to draw oil in through the inlet(s). Reducing the restriction to the fluid getting to the cavity improves the efficiency of the pump and helps avoid cavitation.

The original configuration is designed to adequately supply the pump requirements at normal RPM levels. Double - or even approach triple - the speed of the pump while using original sized inlet plumbing creates multiple issues.

Anything you do to reduce that restriction to the fluid being drawn into the vacuum created between the rotors, including allowing that fluid to enter both sides of the open space, will help make the pump work more efficiently and without cavitation.