I can only guess, But I think the reason joker sets do not adress assistance are becuase they are for the main lift. Assistance are based of plan and feel and not necessarily percentage. I use joker sets only as singles. I know in the beyond program they are used as 5s and 3s in those weeks, but just personally even in those weeks I only do them as singles.
I.E last bench day I did 245 for 14 medium grip. Felt good so afterward I did 255 for a single, then 275 for a single. Couldve worked up more but found it counter productive. By the time I got to 275 it felt “light” compared to the last time I did It. Thats all I need with these sets.
For bench, at my current max, I can gage my progress based on how 275 feels, if it comes off the chest fast i know im doing well…in a couple cycles my new gage weight might be 295…If that blasts up off my chest im good I do not need to do more singles even though I can probably get 320 for a single…Little vague but hope that helps