The return regulator (carb) I have says to check the return line size by running all fuel bypassed (unscrewed 4 turns) with carb lines plugged (no flow on needle/seat).
The pressure at the regulator port should be less than 3 psi. Mine was 1.8 psi
Thinking about it. If the pressure is too high, it will push open the needle and seat at idle. And the regulator needs some margin to avoid fluctuation.

1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1