There is a power factor for each phase, but as the motor behaves symmetrically between the three phases, that is, between each of them there are 120 electrical degrees, it must be the same, unless you use it as single phase. I have always seen the three-phase capacitors, and I say I have seen them because I have disassembled them to see them inside, connected in a triangle, not in a star, because in this way they are each directly connected to the line that is their objective, because in star they would remain Always two of them connected in series through the neutral point.