Why is torque falling at low speed?

I'm running the motor in torque mode with an encoder. It works really well.

The only problem I have is that something internal to the FOC software adjusts the torque down at (very) low and zero speed. I assume this is done to avoid the motor overheating.

Example:

I align and start the motor, it quickly spins up and draws 20W. Lots of torque.

I apply some friction to the motor and it still draws approx 20W.

I apply more and more friction, the speed falls as I apply more friction. At some point when the speed gets low the power draw gradually falls.

I force the motor to a complete stop, the power draw is almost zero. Almost zero torque obviously.

I let go of the motor, it spins up again and draws 20W.

So my questions are pretty simple:

- What is affecting my torque at low/zero speeds?

- How do I increase torque at low/zero speeds?

Any pointers are greatly appreciated.