I tried to use the -clKernel 3 option (Phoenix 5.7b) for various drivers from 18.6.1 to 21 .... but on each of these drivers -clKernel 3 is ignored for all GPU (RX580 Nitro+ 8GB Micron and Hynix cards)
Same here with MSI RX 580 8 Go Armor without 'clkernel 3' I get 32-33 Mh/s