I was recently told by a technical department that an ac system that is short of refrigerant would be more apparent in HEAT mode rather than COOL mode; based on air on/off temperatures on indoor units.

I always understood that HEAT mode used heat of compression as well as phase-change to generate really efficient heating that demanded less power input. And in COOL mode you relied only on refrigerant phase-change for cooling effect.

Can someone please explain this to me?
Thanks