Keep in mind that this is a mechanical, fluid dynamic, and thermal dynamic problem.

If you increase extrusion rate, then one one or more of the following needs to change.

increase the hot end temperature lower the part cooling fan speed increase the nozzle diameter

the extrusion/flow rate multiplier (slicers have various names for it) is nothing more than a fudge factor that allows you to make a tweak without changing one of the above.

Calculating your e steps at 1 mm/s will minimize the the fluid dynamic and thermal dynamic variables at play.

If you want to completely remove fluid dynamic and thermal dynamic variables, disconnect the extruder from the hotend. That way the only thing you're dealing with are mechanical variables.