Sometimes setting the pressure high at idle results in larger drop in pressure.

It depends on how the regulator is designed and the fuel pump pressure and flow rate (gals/min) relationship.
A deadheaded pump is delivering close to zero gallons per minute at idle.

It is going to depend on the regulator pressure and the flows and pressures it will see (ie the the pump).

We took a look at a couple different regulators, and then the effect of control pressures and flow rates in this thread.
https://www.forabodiesonly.com/mopa...b-stumble.437541/page-20#post-1972625252
(read down from that post for pump output volume and cudafever's tests)

You can probably test in a similar manner, but start with the pump data from the manufacturer.
There's some basic rules of thumb for fuel consumption, and you can also look at engine dyno data for similar engines.