Just my take...

When I used to fly the BE-1900 I set the power via Torque, with two notable exceptions:

1) ITT when temperature limited in the climb (think old BE-1900C model)

2) Fuel flow with an MEL'd fuel guage

As for a reference Airplane Flying Handbook 14-7 (FAA-H-8083-3A) or the procedures/performance sections of the respective flight manual.

From my perspective if he/she is PF then they can set the power any way they like (within reason). I would be curious what their reasoning is. Is it a maintenance/save the engine type mentality?

WJI