In the motors I use, bafang BBHD (1KW nominal), its possible to just throttle down the motor, there are a number of power levels programed into motors, the one on my main bike mentioned is set with eight levels, the bike has 8 mechanical gears in a shimano nexus hub, and I put a tiny chain wheel on the motor mounted on the bottom bracket to get useful torque in every gear, the original chain wheel on the motor was way too big for the motor to drive the bike efficiently I think, but the penalty is that the pedals spindle turns much faster than anybody would pedal.
If the motor power setting is kept low, it's possible to pedal motor assisted at lower speed in higher gears, but I suspect the motor might be running inefficiently at lower speeds, so the power transfer between rider and motor probably isn't fair, the motor would be likely to waste more energy at lower speeds I think.
I don't know if the same characteristic would apply to lower power motors, even though they have to help the pedaller, I suspect the same lower motor-pedal speed rate necessary to assist human pedalling speed might result in lower motor efficiency. It's something to be aware of, and probably worth investigating in your study.
I'd be interested to know the results :)