How much PhiX should I spike in to my library before sequencing?

• NextSeq 1000/2000: 5% PhiX spike-in
• NextSeq 500/550: 5% PhiX spike-in
• NovaSeq 6000: 

     - 5% PhiX spike-in when pooling with non-Curio Seeker libraries 
     - 10% PhiX spike-in when pooling with only Curio Seeker libraries