The controller uses Pulse Width Modulation
(PWM) to effectively regulate the voltage being sent to the motor's phase windings.
The actual current being drawn will depend on the torsional load acting upon the motor. The harder the motor has to work, the greater the current draw will be.
The controller is able to monitor the current being drawn by measuring the voltage drop across a measured resistance
(the shunt).
As the current being drawn by the motor starts to rise, the voltage drop across the shunt
(which is constantly being monitored by the controller) will also rise. If the voltage drop starts to exceed the maximum set voltage, the controller will automatically reduce the width of the voltage pulses, which will simultaneously reduce the current being delivered to the motor to prevent it from working too hard.
How can I force the motor to consume about 10-15Amps when the bicycle in a "upside-down" position?
To increase the current, you will need to increase the load on the motor, this can be done by disconnecting the brake switch and applying the brakes, but your brake pads and wheel rim
(or brake disc) will get very hot if you load it for too long.
Alan