Well (again, this has been stated since the original 5/3/1 so I don't think it's some kind of secret content), as a rule of thumb 5 solid reps = 85%TM; 3 solid reps = 90%TM. Regardless of how many reps you COULD do, once you hit the number you want to hit you stop and that's your TM, you do NOT increase more than the usual 10/5 lbs.
Also, regardless of the program you're doing, your numbers during each cycle should give you some input if you're working with the correct loads or not (it's especially obvious when doing PR sets and/or Jokers).
I.e., I've just finished a cycle.
My TM on deads was 146kg, on 1+ week I've hit 9 solid reps @ 140kg. Then followed with 2 sets of 3 Jokers @ 152kg.
For next cycle, my TM has to be increased to 150kg (4kg = 10lbs), so next week I'm doing the TM test for 150kg - I have to hit 5 solid reps with 150kg, that's the TM I want (85%).
Now, I know that if I can do 140x9 and follow up with 2 sets of 152x3 after the AMRAP set, I can realistically do at least 7-8 reps @ 150kg while fresh. But once I hit the 5 reps, that's it, the test ends and I'm not increasing the TM anymore than the 4kg (10lbs) from 146 to 150kg. It means my TM is correct to go ahead.
There's a bit more talk about it here: